diff --git a/schema/schema.definition.sql b/schema/schema.definition.sql
index d35a250..31087be 100644
--- a/schema/schema.definition.sql
+++ b/schema/schema.definition.sql
@@ -993,21 +993,33 @@ COMMENT ON FUNCTION maevsi.events_organized() IS 'Add a function that returns al
 CREATE FUNCTION maevsi.invitation_claim_array() RETURNS uuid[]
     LANGUAGE plpgsql STABLE STRICT
     AS $$
+DECLARE
+  _arr UUID[];
+  _result_arr UUID[] := ARRAY[]::UUID[];
+  _id UUID;
 BEGIN
-  RETURN string_to_array(replace(btrim(current_setting('jwt.claims.invitations', true), '[]'), '"', ''), ',')::UUID[];
+  _arr := string_to_array(replace(btrim(current_setting('jwt.claims.invitations', true), '[]'), '"', ''), ',')::UUID[];
+  FOREACH _id IN ARRAY arr
+  LOOP
+    -- omit invitations authored by a blocked account
+   IF NOT EXISTS(
+	  SELECT 1
+	  FROM maevsi.invitation i
+	    JOIN maevsi.contact c ON i.contact_id = c.contact_id
+	    JOIN maevsi.account_block b ON c.author_account_id = b.blocked_account_id
+	  WHERE i.id = _id and b.author_account_id = current_setting('jwt.claims.account_id', true)
+	) THEN
+      _result_arr := append_array(result_arr, _id);
+	END IF;
+  END LOOP;
+
+  RETURN _result_arr;
 END
 $$;
 
 
 ALTER FUNCTION maevsi.invitation_claim_array() OWNER TO postgres;
 
---
--- Name: FUNCTION invitation_claim_array(); Type: COMMENT; Schema: maevsi; Owner: postgres
---
-
-COMMENT ON FUNCTION maevsi.invitation_claim_array() IS 'Returns the current invitation claims as UUID array.';
-
-
 --
 -- Name: invitation_contact_ids(); Type: FUNCTION; Schema: maevsi; Owner: postgres
 --
@@ -1019,7 +1031,17 @@ BEGIN
   RETURN QUERY
     SELECT invitation.contact_id FROM maevsi.invitation
     WHERE id = ANY (maevsi.invitation_claim_array())
-    OR    event_id IN (SELECT maevsi.events_organized());
+    OR (
+	   event_id IN (SELECT maevsi.events_organized())
+	   AND
+	   -- omit contacts authored by a blocked account or referring to a blocked account
+	   contact_id NOT IN (
+		 SELECT c.id
+		 FROM maevsi.contact c
+		   JOIN maevsi.account_block b ON c.author_account_id = b.blocked_account_id OR c.account_id = b.blocked_account_id
+		 WHERE b.author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	   )
+	);
 END;
 $$;
 
@@ -1319,7 +1341,7 @@ DECLARE
   whitelisted_cols TEXT[] := ARRAY['feedback', 'feedback_paper'];
 BEGIN
   IF
-      TG_OP = 'UPDATE'
+    TG_OP = 'UPDATE'
     AND ( -- Invited.
       OLD.id = ANY (maevsi.invitation_claim_array())
       OR
@@ -1521,17 +1543,25 @@ BEGIN
   jwt_account_id := NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID;
 
   RETURN QUERY
-  SELECT invitation.event_id FROM maevsi.invitation
+  SELECT event_id FROM maevsi.invitation
   WHERE
-      invitation.contact_id IN (
+    (
+      contact_id IN (
         SELECT id
         FROM maevsi.contact
         WHERE
-          jwt_account_id IS NOT NULL
-          AND
-          contact.account_id = jwt_account_id
-      ) -- The contact selection does not return rows where account_id "IS" null due to the equality comparison.
-  OR  invitation.id = ANY (maevsi.invitation_claim_array());
+          account_id = jwt_account_id
+		  -- The contact selection does not return rows where account_id "IS" null due to the equality comparison.
+		  AND
+		  -- contact not created by a blocked account
+		  author_account_id NOT IN (
+			SELECT account_block_id
+			FROM maevsi.account_block
+		    WHERE b.author_account_id = jwt_account_id
+		  )
+		)
+    )
+    OR id = ANY (maevsi.invitation_claim_array());
 END
 $$;
 
@@ -1579,6 +1609,58 @@ COMMENT ON COLUMN maevsi.account.id IS 'The account''s internal id.';
 COMMENT ON COLUMN maevsi.account.username IS 'The account''s username.';
 
 
+--
+-- Name: account_block; Type: TABLE; Schema: maevsi; Owner: postgres
+--
+
+CREATE TABLE maevsi.account_block (
+    id uuid DEFAULT gen_random_uuid() NOT NULL,
+    author_account_id uuid NOT NULL,
+    blocked_account_id uuid NOT NULL,
+    created_at timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+    CONSTRAINT account_block_check CHECK ((author_account_id <> blocked_account_id))
+);
+
+
+ALTER TABLE maevsi.account_block OWNER TO postgres;
+
+--
+-- Name: TABLE account_block; Type: COMMENT; Schema: maevsi; Owner: postgres
+--
+
+COMMENT ON TABLE maevsi.account_block IS '@omit update,delete
+Blocking of an account by another account.';
+
+
+--
+-- Name: COLUMN account_block.id; Type: COMMENT; Schema: maevsi; Owner: postgres
+--
+
+COMMENT ON COLUMN maevsi.account_block.id IS '@omit create\nThe blocking''s internal id.';
+
+
+--
+-- Name: COLUMN account_block.author_account_id; Type: COMMENT; Schema: maevsi; Owner: postgres
+--
+
+COMMENT ON COLUMN maevsi.account_block.author_account_id IS 'The id of the user who created the blocking.';
+
+
+--
+-- Name: COLUMN account_block.blocked_account_id; Type: COMMENT; Schema: maevsi; Owner: postgres
+--
+
+COMMENT ON COLUMN maevsi.account_block.blocked_account_id IS 'The id of the account to be blocked.';
+
+
+--
+-- Name: COLUMN account_block.created_at; Type: COMMENT; Schema: maevsi; Owner: postgres
+--
+
+COMMENT ON COLUMN maevsi.account_block.created_at IS '@omit update,delete
+The timestamp when the blocking was created.';
+
+
 --
 -- Name: achievement; Type: TABLE; Schema: maevsi; Owner: postgres
 --
@@ -2877,6 +2959,22 @@ COMMENT ON COLUMN sqitch.tags.planner_name IS 'Name of the user who planed the t
 COMMENT ON COLUMN sqitch.tags.planner_email IS 'Email address of the user who planned the tag.';
 
 
+--
+-- Name: account_block account_block_author_account_id_blocked_account_id_key; Type: CONSTRAINT; Schema: maevsi; Owner: postgres
+--
+
+ALTER TABLE ONLY maevsi.account_block
+    ADD CONSTRAINT account_block_author_account_id_blocked_account_id_key UNIQUE (author_account_id, blocked_account_id);
+
+
+--
+-- Name: account_block account_block_pkey; Type: CONSTRAINT; Schema: maevsi; Owner: postgres
+--
+
+ALTER TABLE ONLY maevsi.account_block
+    ADD CONSTRAINT account_block_pkey PRIMARY KEY (id);
+
+
 --
 -- Name: account account_pkey; Type: CONSTRAINT; Schema: maevsi; Owner: postgres
 --
@@ -3322,6 +3420,22 @@ CREATE TRIGGER maevsi_private_account_email_address_verification_valid_until BEF
 CREATE TRIGGER maevsi_private_account_password_reset_verification_valid_until BEFORE INSERT OR UPDATE OF password_reset_verification ON maevsi_private.account FOR EACH ROW EXECUTE FUNCTION maevsi_private.account_password_reset_verification_valid_until();
 
 
+--
+-- Name: account_block account_block_author_account_id_fkey; Type: FK CONSTRAINT; Schema: maevsi; Owner: postgres
+--
+
+ALTER TABLE ONLY maevsi.account_block
+    ADD CONSTRAINT account_block_author_account_id_fkey FOREIGN KEY (author_account_id) REFERENCES maevsi.account(id);
+
+
+--
+-- Name: account_block account_block_blocked_account_id_fkey; Type: FK CONSTRAINT; Schema: maevsi; Owner: postgres
+--
+
+ALTER TABLE ONLY maevsi.account_block
+    ADD CONSTRAINT account_block_blocked_account_id_fkey FOREIGN KEY (blocked_account_id) REFERENCES maevsi.account(id);
+
+
 --
 -- Name: account account_id_fkey; Type: FK CONSTRAINT; Schema: maevsi; Owner: postgres
 --
@@ -3528,6 +3642,26 @@ ALTER TABLE ONLY sqitch.tags
 
 ALTER TABLE maevsi.account ENABLE ROW LEVEL SECURITY;
 
+--
+-- Name: account_block; Type: ROW SECURITY; Schema: maevsi; Owner: postgres
+--
+
+ALTER TABLE maevsi.account_block ENABLE ROW LEVEL SECURITY;
+
+--
+-- Name: account_block account_block_insert; Type: POLICY; Schema: maevsi; Owner: postgres
+--
+
+CREATE POLICY account_block_insert ON maevsi.account_block FOR INSERT WITH CHECK ((((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)));
+
+
+--
+-- Name: account_block account_block_select; Type: POLICY; Schema: maevsi; Owner: postgres
+--
+
+CREATE POLICY account_block_select ON maevsi.account_block FOR SELECT USING ((((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)));
+
+
 --
 -- Name: account account_select; Type: POLICY; Schema: maevsi; Owner: postgres
 --
@@ -3565,21 +3699,29 @@ CREATE POLICY contact_delete ON maevsi.contact FOR DELETE USING ((((NULLIF(curre
 -- Name: contact contact_insert; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY contact_insert ON maevsi.contact FOR INSERT WITH CHECK ((((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)));
+CREATE POLICY contact_insert ON maevsi.contact FOR INSERT WITH CHECK (((author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid) AND (NOT (account_id IN ( SELECT account_block.blocked_account_id
+   FROM maevsi.account_block
+  WHERE (account_block.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))))));
 
 
 --
 -- Name: contact contact_select; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY contact_select ON maevsi.contact FOR SELECT USING (((((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND ((account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid) OR (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))) OR (id IN ( SELECT maevsi.invitation_contact_ids() AS invitation_contact_ids))));
+CREATE POLICY contact_select ON maevsi.contact FOR SELECT USING ((((account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid) AND (NOT (author_account_id IN ( SELECT account_block.blocked_account_id
+   FROM maevsi.account_block
+  WHERE (account_block.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))))) OR ((author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid) AND (NOT (account_id IN ( SELECT account_block.blocked_account_id
+   FROM maevsi.account_block
+  WHERE (account_block.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))))) OR (id IN ( SELECT maevsi.invitation_contact_ids() AS invitation_contact_ids))));
 
 
 --
 -- Name: contact contact_update; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY contact_update ON maevsi.contact FOR UPDATE USING ((((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)));
+CREATE POLICY contact_update ON maevsi.contact FOR UPDATE USING (((author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid) AND (NOT (account_id IN ( SELECT account_block.blocked_account_id
+   FROM maevsi.account_block
+  WHERE (account_block.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))))));
 
 
 --
@@ -3611,7 +3753,9 @@ CREATE POLICY event_insert ON maevsi.event FOR INSERT WITH CHECK ((((NULLIF(curr
 -- Name: event event_select; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY event_select ON maevsi.event FOR SELECT USING ((((visibility = 'public'::maevsi.event_visibility) AND ((invitee_count_maximum IS NULL) OR (invitee_count_maximum > maevsi.invitee_count(id)))) OR (((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)) OR (id IN ( SELECT maevsi_private.events_invited() AS events_invited))));
+CREATE POLICY event_select ON maevsi.event FOR SELECT USING ((((visibility = 'public'::maevsi.event_visibility) AND ((invitee_count_maximum IS NULL) OR (invitee_count_maximum > maevsi.invitee_count(id))) AND (NOT (author_account_id IN ( SELECT account_block.blocked_account_id
+   FROM maevsi.account_block
+  WHERE (account_block.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))))) OR (author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid) OR (id IN ( SELECT maevsi_private.events_invited() AS events_invited))));
 
 
 --
@@ -3638,27 +3782,48 @@ CREATE POLICY invitation_delete ON maevsi.invitation FOR DELETE USING ((event_id
 -- Name: invitation invitation_insert; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY invitation_insert ON maevsi.invitation FOR INSERT WITH CHECK (((event_id IN ( SELECT maevsi.events_organized() AS events_organized)) AND ((maevsi.event_invitee_count_maximum(event_id) IS NULL) OR (maevsi.event_invitee_count_maximum(event_id) > maevsi.invitee_count(event_id))) AND (((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (contact_id IN ( SELECT contact.id
+CREATE POLICY invitation_insert ON maevsi.invitation FOR INSERT WITH CHECK (((event_id IN ( SELECT maevsi.events_organized() AS events_organized)) AND ((maevsi.event_invitee_count_maximum(event_id) IS NULL) OR (maevsi.event_invitee_count_maximum(event_id) > maevsi.invitee_count(event_id))) AND (contact_id IN ( SELECT contact.id
    FROM maevsi.contact
-  WHERE (contact.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))))));
+  WHERE (contact.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)
+EXCEPT
+ SELECT c.id
+   FROM (maevsi.contact c
+     JOIN maevsi.account_block b ON (((c.account_id = b.blocked_account_id) AND (c.author_account_id = b.author_account_id))))
+  WHERE (c.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)))));
 
 
 --
 -- Name: invitation invitation_select; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY invitation_select ON maevsi.invitation FOR SELECT USING (((id = ANY (maevsi.invitation_claim_array())) OR (((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (contact_id IN ( SELECT contact.id
+CREATE POLICY invitation_select ON maevsi.invitation FOR SELECT USING (((id = ANY (maevsi.invitation_claim_array())) OR (contact_id IN ( SELECT contact.id
    FROM maevsi.contact
-  WHERE (contact.account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)))) OR (event_id IN ( SELECT maevsi.events_organized() AS events_organized))));
+  WHERE (contact.account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)
+EXCEPT
+ SELECT c.id
+   FROM (maevsi.contact c
+     JOIN maevsi.account_block b ON (((c.account_id = b.author_account_id) AND (c.author_account_id = b.blocked_account_id))))
+  WHERE (c.account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))) OR ((event_id IN ( SELECT maevsi.events_organized() AS events_organized)) AND (NOT (contact_id IN ( SELECT c.id
+   FROM (maevsi.contact c
+     JOIN maevsi.account_block b ON (((c.author_account_id = b.blocked_account_id) OR (c.account_id = b.blocked_account_id))))
+  WHERE (b.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)))))));
 
 
 --
 -- Name: invitation invitation_update; Type: POLICY; Schema: maevsi; Owner: postgres
 --
 
-CREATE POLICY invitation_update ON maevsi.invitation FOR UPDATE USING (((id = ANY (maevsi.invitation_claim_array())) OR (((NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid IS NOT NULL) AND (contact_id IN ( SELECT contact.id
+CREATE POLICY invitation_update ON maevsi.invitation FOR UPDATE USING (((id = ANY (maevsi.invitation_claim_array())) OR (contact_id IN ( SELECT contact.id
    FROM maevsi.contact
-  WHERE (contact.account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)))) OR (event_id IN ( SELECT maevsi.events_organized() AS events_organized))));
+  WHERE (contact.account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)
+EXCEPT
+ SELECT c.id
+   FROM (maevsi.contact c
+     JOIN maevsi.account_block b ON (((c.account_id = b.author_account_id) AND (c.author_account_id = b.blocked_account_id))))
+  WHERE (c.account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid))) OR ((event_id IN ( SELECT maevsi.events_organized() AS events_organized)) AND (NOT (contact_id IN ( SELECT c.id
+   FROM (maevsi.contact c
+     JOIN maevsi.account_block b ON (((c.author_account_id = b.blocked_account_id) OR (c.account_id = b.blocked_account_id))))
+  WHERE (b.author_account_id = (NULLIF(current_setting('jwt.claims.account_id'::text, true), ''::text))::uuid)))))));
 
 
 --
@@ -4321,6 +4486,13 @@ GRANT SELECT ON TABLE maevsi.account TO maevsi_account;
 GRANT SELECT ON TABLE maevsi.account TO maevsi_anonymous;
 
 
+--
+-- Name: TABLE account_block; Type: ACL; Schema: maevsi; Owner: postgres
+--
+
+GRANT SELECT,INSERT ON TABLE maevsi.account_block TO maevsi_account;
+
+
 --
 -- Name: TABLE achievement; Type: ACL; Schema: maevsi; Owner: postgres
 --
diff --git a/src/deploy/function_events_invited.sql b/src/deploy/function_events_invited.sql
index 7fff04b..b07fc5c 100644
--- a/src/deploy/function_events_invited.sql
+++ b/src/deploy/function_events_invited.sql
@@ -4,32 +4,43 @@
 -- requires: schema_public
 -- requires: table_invitation
 -- requires: table_contact
+-- requires: table_account_block
 -- requires: role_account
 -- requires: role_anonymous
 
 BEGIN;
 
-CREATE FUNCTION maevsi_private.events_invited()
-RETURNS TABLE (event_id UUID) AS $$
+CREATE OR REPLACE FUNCTION maevsi_private.events_invited()
+  RETURNS TABLE(event_id uuid)
+AS $$
 DECLARE
   jwt_account_id UUID;
 BEGIN
   jwt_account_id := NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID;
 
   RETURN QUERY
-  SELECT invitation.event_id FROM maevsi.invitation
+  SELECT event_id FROM maevsi.invitation
   WHERE
-      invitation.contact_id IN (
+    (
+      contact_id IN (
         SELECT id
         FROM maevsi.contact
         WHERE
-          jwt_account_id IS NOT NULL
-          AND
-          contact.account_id = jwt_account_id
-      ) -- The contact selection does not return rows where account_id "IS" null due to the equality comparison.
-  OR  invitation.id = ANY (maevsi.invitation_claim_array());
+          account_id = jwt_account_id
+		  -- The contact selection does not return rows where account_id "IS" null due to the equality comparison.
+		  AND
+		  -- contact not created by a blocked account
+		  author_account_id NOT IN (
+			SELECT account_block_id
+			FROM maevsi.account_block
+		    WHERE b.author_account_id = jwt_account_id
+		  )
+		)
+    )
+    OR id = ANY (maevsi.invitation_claim_array());
 END
-$$ LANGUAGE PLPGSQL STRICT STABLE SECURITY DEFINER;
+$$ LANGUAGE plpgsql STABLE STRICT SECURITY DEFINER
+;
 
 COMMENT ON FUNCTION maevsi_private.events_invited() IS 'Add a function that returns all event ids for which the invoker is invited.';
 
diff --git a/src/deploy/function_invitation_claim_array.sql b/src/deploy/function_invitation_claim_array.sql
index 05a122a..365833a 100644
--- a/src/deploy/function_invitation_claim_array.sql
+++ b/src/deploy/function_invitation_claim_array.sql
@@ -1,20 +1,40 @@
 -- Deploy maevsi:function_invitation_claim_array to pg
 -- requires: privilege_execute_revoke
 -- requires: schema_public
+-- requires: table_invitation
+-- requires: table_contact
+-- requires: table_account_block
 -- requires: role_account
 -- requires: role_anonymous
 
 BEGIN;
 
-CREATE FUNCTION maevsi.invitation_claim_array()
+CREATE OR REPLACE FUNCTION maevsi.invitation_claim_array()
 RETURNS UUID[] AS $$
+DECLARE
+  _arr UUID[];
+  _result_arr UUID[] := ARRAY[]::UUID[];
+  _id UUID;
 BEGIN
-  RETURN string_to_array(replace(btrim(current_setting('jwt.claims.invitations', true), '[]'), '"', ''), ',')::UUID[];
+  _arr := string_to_array(replace(btrim(current_setting('jwt.claims.invitations', true), '[]'), '"', ''), ',')::UUID[];
+  FOREACH _id IN ARRAY arr
+  LOOP
+    -- omit invitations authored by a blocked account
+   IF NOT EXISTS(
+	  SELECT 1
+	  FROM maevsi.invitation i
+	    JOIN maevsi.contact c ON i.contact_id = c.contact_id
+	    JOIN maevsi.account_block b ON c.author_account_id = b.blocked_account_id
+	  WHERE i.id = _id and b.author_account_id = current_setting('jwt.claims.account_id', true)
+	) THEN
+      _result_arr := append_array(result_arr, _id);
+	END IF;
+  END LOOP;
+
+  RETURN _result_arr;
 END
 $$ LANGUAGE PLPGSQL STRICT STABLE SECURITY INVOKER;
 
-COMMENT ON FUNCTION maevsi.invitation_claim_array() IS 'Returns the current invitation claims as UUID array.';
-
 GRANT EXECUTE ON FUNCTION maevsi.invitation_claim_array() TO maevsi_account, maevsi_anonymous;
 
 COMMIT;
diff --git a/src/deploy/function_invitation_contact_ids.sql b/src/deploy/function_invitation_contact_ids.sql
index 11bd513..e3f0f9b 100644
--- a/src/deploy/function_invitation_contact_ids.sql
+++ b/src/deploy/function_invitation_contact_ids.sql
@@ -2,6 +2,8 @@
 -- requires: privilege_execute_revoke
 -- requires: schema_public
 -- requires: table_invitation
+-- requires: table_contact
+-- requires: table_account_block
 -- requires: function_invitation_claim_array
 -- requires: function_events_organized
 -- requires: role_account
@@ -9,13 +11,23 @@
 
 BEGIN;
 
-CREATE FUNCTION maevsi.invitation_contact_ids()
+CREATE OR REPLACE FUNCTION maevsi.invitation_contact_ids()
 RETURNS TABLE (contact_id UUID) AS $$
 BEGIN
   RETURN QUERY
     SELECT invitation.contact_id FROM maevsi.invitation
     WHERE id = ANY (maevsi.invitation_claim_array())
-    OR    event_id IN (SELECT maevsi.events_organized());
+    OR (
+	   event_id IN (SELECT maevsi.events_organized())
+	   AND
+	   -- omit contacts authored by a blocked account or referring to a blocked account
+	   contact_id NOT IN (
+		 SELECT c.id
+		 FROM maevsi.contact c
+		   JOIN maevsi.account_block b ON c.author_account_id = b.blocked_account_id OR c.account_id = b.blocked_account_id
+		 WHERE b.author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	   )
+	);
 END;
 $$ LANGUAGE PLPGSQL STRICT STABLE SECURITY DEFINER;
 
diff --git a/src/deploy/table_account_block.sql b/src/deploy/table_account_block.sql
new file mode 100644
index 0000000..8182dbe
--- /dev/null
+++ b/src/deploy/table_account_block.sql
@@ -0,0 +1,22 @@
+-- Deploy maevsi:table_account_block to pg
+-- requires: schema_public
+-- requires: table_account_public
+
+BEGIN;
+
+CREATE TABLE maevsi.account_block (
+  id                  UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  author_account_id   UUID NOT NULL REFERENCES maevsi.account(id),
+  blocked_account_id  UUID NOT NULL REFERENCES maevsi.account(id),
+  created_at          TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  UNIQUE (author_account_id, blocked_account_id),
+  CHECK (author_account_id != blocked_account_id)
+);
+
+COMMENT ON TABLE maevsi.account_block IS E'@omit update,delete\nBlocking of an account by another account.';
+COMMENT ON COLUMN maevsi.account_block.id IS '@omit create\nThe blocking''s internal id.';
+COMMENT ON COLUMN maevsi.account_block.author_account_id IS 'The id of the user who created the blocking.';
+COMMENT ON COLUMN maevsi.account_block.blocked_account_id IS 'The id of the account to be blocked.';
+COMMENT ON COLUMN maevsi.account_block.created_at IS E'@omit update,delete\nThe timestamp when the blocking was created.';
+
+COMMIT;
diff --git a/src/deploy/table_account_block_policy.sql b/src/deploy/table_account_block_policy.sql
new file mode 100644
index 0000000..c2d45c4
--- /dev/null
+++ b/src/deploy/table_account_block_policy.sql
@@ -0,0 +1,26 @@
+-- Deploy maevsi:table_account_block_policy to pg
+-- requires: schema_public
+-- requires: table_account_block
+-- requires: role_account
+
+BEGIN;
+
+GRANT INSERT, SELECT ON TABLE maevsi.account_block TO maevsi_account;
+
+ALTER TABLE maevsi.account_block ENABLE ROW LEVEL SECURITY;
+
+-- Only allow inserts for blocked accounts authored by the current user.
+CREATE POLICY account_block_insert ON maevsi.account_block FOR INSERT WITH CHECK (
+  NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
+  AND
+  author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+);
+
+-- Only allow selects for blocked accounts authored by the current user.
+CREATE POLICY account_block_select ON maevsi.account_block FOR SELECT USING (
+  NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
+  AND
+  author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+);
+
+COMMIT;
diff --git a/src/deploy/table_contact_policy.sql b/src/deploy/table_contact_policy.sql
index 5be8989..8652d14 100644
--- a/src/deploy/table_contact_policy.sql
+++ b/src/deploy/table_contact_policy.sql
@@ -1,5 +1,6 @@
 -- Deploy maevsi:table_contact_policy to pg
 -- requires: schema_public
+-- requires: table_account_block
 -- requires: table_contact
 -- requires: role_account
 -- requires: role_anonymous
@@ -12,34 +13,52 @@ GRANT INSERT, UPDATE, DELETE ON TABLE maevsi.contact TO maevsi_account;
 
 ALTER TABLE maevsi.contact ENABLE ROW LEVEL SECURITY;
 
--- Only display contacts referencing the invoker's account.
--- Only display contacts authored by the invoker's account.
--- Only display contacts for which an accessible invitation exists.
+-- Only display contacts referencing the invoker's account, omit contacts authored by a blocked account.
+-- Only display contacts authored by the invoker's account, omit contacts referring to a blocked account.
+-- Only display contacts for which an accessible invitation exists, omit contacts auhored by a blocked account or referring to a blocked account.
 CREATE POLICY contact_select ON maevsi.contact FOR SELECT USING (
   (
-    NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
-    AND (
-      account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
-      OR
+	  account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	  AND
+	  author_account_id NOT IN (
+		  SELECT blocked_account_id
+		  FROM maevsi.account_block
+		  WHERE author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	  )
+	)
+	OR
+	(
       author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
-    )
-  )
-  OR
-  id IN (SELECT maevsi.invitation_contact_ids())
+	  AND
+	  account_id NOT IN (
+		  SELECT blocked_account_id
+		  FROM maevsi.account_block
+		  WHERE author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	  )
+	)
+    OR id IN (SELECT maevsi.invitation_contact_ids())
 );
 
--- Only allow inserts for contacts authored by the invoker's account.
+-- Only allow inserts for contacts authored by the invoker's account
+-- No blocked account can be invited
 CREATE POLICY contact_insert ON maevsi.contact FOR INSERT WITH CHECK (
-  NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
-  AND
   author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+  AND account_id NOT IN (
+	SELECT blocked_account_id
+	FROM maevsi.account_block
+	WHERE author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+  )
 );
 
 -- Only allow updates for contacts authored by the invoker's account.
+-- No contact referring to a blocked account can be updated
 CREATE POLICY contact_update ON maevsi.contact FOR UPDATE USING (
-  NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
-  AND
   author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+  AND account_id NOT IN (
+	SELECT blocked_account_id
+	FROM maevsi.account_block
+	WHERE author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+  )
 );
 
 -- Only allow deletes for contacts authored by the invoker's account except for the own account's contact.
diff --git a/src/deploy/table_event_policy.sql b/src/deploy/table_event_policy.sql
index 5c63988..63f1f0f 100644
--- a/src/deploy/table_event_policy.sql
+++ b/src/deploy/table_event_policy.sql
@@ -1,6 +1,7 @@
 -- Deploy maevsi:table_event_policy to pg
 -- requires: schema_public
 -- requires: table_event
+-- requires: table_account_block
 -- requires: role_account
 -- requires: role_anonymous
 -- requires: schema_private
@@ -13,26 +14,31 @@ GRANT INSERT, UPDATE, DELETE ON TABLE maevsi.event TO maevsi_account;
 
 ALTER TABLE maevsi.event ENABLE ROW LEVEL SECURITY;
 
--- Only display events that are public and not full.
+-- Only display events that are public and not full and not organized by a blocked account
 -- Only display events that are organized by oneself.
--- Only display events to which oneself is invited.
+-- Only display events to which oneself is invited, but not by an invitation authored by a blocked account
 CREATE POLICY event_select ON maevsi.event FOR SELECT USING (
 -- Below copied to function `maevsi.event_invitee_count_maximum`.
-      (
-        visibility = 'public'
-        AND
-        (
-          invitee_count_maximum IS NULL
-          OR
-          invitee_count_maximum > (maevsi.invitee_count(id)) -- Using the function here is required as there would otherwise be infinite recursion.
-        )
-      )
-  OR  (
-    NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
+  (
+    visibility = 'public'
     AND
-    author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+    (
+      invitee_count_maximum IS NULL
+      OR
+      invitee_count_maximum > (maevsi.invitee_count(id)) -- Using the function here is required as there would otherwise be infinite recursion.
+    )
+		AND author_account_id NOT IN (
+			SELECT blocked_account_id
+			FROM maevsi.account_block
+			WHERE author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+		)
   )
-  OR  id IN (SELECT maevsi_private.events_invited())
+	OR (
+		author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	)
+  OR (
+		id IN (SELECT maevsi_private.events_invited())
+	)
 );
 
 -- Only allow inserts for events authored by the current user.
diff --git a/src/deploy/table_invitation_policy.sql b/src/deploy/table_invitation_policy.sql
index c333693..4f61ea6 100644
--- a/src/deploy/table_invitation_policy.sql
+++ b/src/deploy/table_invitation_policy.sql
@@ -1,6 +1,8 @@
 -- Deploy maevsi:table_invitation_policy to pg
 -- requires: schema_public
 -- requires: table_invitation
+-- requires: table_contact
+-- requires: table_account_block
 -- requires: role_account
 -- requires: role_anonymous
 -- requires: function_invitation_claim_array
@@ -14,62 +16,99 @@ GRANT INSERT, DELETE ON TABLE maevsi.invitation TO maevsi_account;
 
 ALTER TABLE maevsi.invitation ENABLE ROW LEVEL SECURITY;
 
--- Only display invitations issued to oneself through invitation claims.
--- Only display invitations issued to oneself through the account.
--- Only display invitations to events organized by oneself.
+-- Only display invitations issued to oneself through invitation claims, omit invitations authored by a blocked user.
+-- Only display invitations issued to oneself through the account and not authored by a blocked user.
+-- Only display invitations to events organized by oneself, omit invitations authored by a blocked user and invitations issued to a blocked user.
 CREATE POLICY invitation_select ON maevsi.invitation FOR SELECT USING (
-      id = ANY (maevsi.invitation_claim_array())
+  id = ANY (maevsi.invitation_claim_array())
   OR
   (
-    NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
-    AND
     contact_id IN (
       SELECT id
       FROM maevsi.contact
-      WHERE contact.account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+      WHERE account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+
+	    EXCEPT
+
+	    -- contacts to oneself authored by a blocked account
+	    SELECT c.id
+	    FROM maevsi.contact c
+	      JOIN maevsi.account_block b ON c.account_id = b.author_account_id AND c.author_account_id = b.blocked_account_id
+	    WHERE c.account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
     )
   )
-  OR  event_id IN (SELECT maevsi.events_organized())
+  OR (
+	  event_id IN (SELECT maevsi.events_organized())
+	AND
+	  contact_id NOT IN (
+	    SELECT c.id
+	    FROM maevsi.contact c
+	      JOIN maevsi.account_block b
+	      -- contact authored by a blocked account OR referring to a blocked account
+	      ON c.author_account_id = b.blocked_account_id OR c.account_id = b.blocked_account_id
+	    WHERE b.author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	  )
+  )
 );
 
 -- Only allow inserts for invitations to events organized by oneself.
 -- Only allow inserts for invitations to events for which the maximum invitee count is not yet reached.
--- Only allow inserts for invitations issued to a contact that was created by oneself.
+-- Only allow inserts for invitations issued to a contact that was created by oneself
+-- Do not allow inserts for invitations issued to a contact referring a blocked account
 CREATE POLICY invitation_insert ON maevsi.invitation FOR INSERT WITH CHECK (
-      event_id IN (SELECT maevsi.events_organized())
+  event_id IN (SELECT maevsi.events_organized())
   AND (
     maevsi.event_invitee_count_maximum(event_id) IS NULL
     OR
     maevsi.event_invitee_count_maximum(event_id) > maevsi.invitee_count(event_id)
   )
   AND
-  (
-    NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
-    AND
     contact_id IN (
       SELECT id
       FROM maevsi.contact
-      WHERE contact.author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
-    )
-  )
+      WHERE author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+
+	    EXCEPT
+
+	    SELECT c.id
+	    FROM maevsi.contact c
+	      JOIN maevsi.account_block b ON c.account_id = b.blocked_account_id and c.author_account_id = b.author_account_id
+	    WHERE c.author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+	  )
 );
 
 -- Only allow updates to invitations issued to oneself through invitation claims.
--- Only allow updates to invitations issued to oneself through the account.
--- Only allow updates to invitations to events organized by oneself.
+-- Only allow updates to invitations issued to oneself through the account, but not invitations auhored by a blocked account
+-- Only allow updates to invitations to events organized by oneself, but not invitations issued to a blocked account or issued by a blocked account
 CREATE POLICY invitation_update ON maevsi.invitation FOR UPDATE USING (
   id = ANY (maevsi.invitation_claim_array())
   OR
   (
-    NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID IS NOT NULL
-    AND
     contact_id IN (
       SELECT id
       FROM maevsi.contact
-      WHERE contact.account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+      WHERE account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+
+	  EXCEPT
+
+	  SELECT c.id
+	  FROM maevsi.contact c
+	    JOIN maevsi.account_block b ON c.account_id = b.author_account_id and c.author_account_id = b.blocked_account_id
+	  WHERE c.account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
+    )
+  )
+  OR
+  (
+    event_id IN (SELECT maevsi.events_organized())
+	  AND
+	  -- omit contacts authored by a blocked account or referring to a blocked account
+    contact_id NOT IN (
+	    SELECT c.id
+	    FROM maevsi.contact c
+	      JOIN maevsi.account_block b ON c.author_account_id = b.blocked_account_id OR c.account_id = b.blocked_account_id
+	    WHERE b.author_account_id = NULLIF(current_setting('jwt.claims.account_id', true), '')::UUID
     )
   )
-  OR  event_id IN (SELECT maevsi.events_organized())
 );
 
 -- Only allow deletes for invitations to events organized by oneself.
@@ -82,7 +121,7 @@ DECLARE
   whitelisted_cols TEXT[] := ARRAY['feedback', 'feedback_paper'];
 BEGIN
   IF
-      TG_OP = 'UPDATE'
+    TG_OP = 'UPDATE'
     AND ( -- Invited.
       OLD.id = ANY (maevsi.invitation_claim_array())
       OR
diff --git a/src/revert/table_account_block.sql b/src/revert/table_account_block.sql
new file mode 100644
index 0000000..77d764a
--- /dev/null
+++ b/src/revert/table_account_block.sql
@@ -0,0 +1,7 @@
+-- Revert maevsi:table_account_block from pg
+
+BEGIN;
+
+DROP TABLE maevsi.account_block;
+
+COMMIT;
diff --git a/src/revert/table_account_block_policy.sql b/src/revert/table_account_block_policy.sql
new file mode 100644
index 0000000..a2efadb
--- /dev/null
+++ b/src/revert/table_account_block_policy.sql
@@ -0,0 +1,8 @@
+-- Revert maevsi:table_account_block_policy from pg
+
+BEGIN;
+
+DROP POLICY account_block_insert ON maevsi.account_block;
+DROP POLICY account_block_select ON maevsi.account_block;
+
+COMMIT;
diff --git a/src/sqitch.plan b/src/sqitch.plan
index 4a6e450..7f3d006 100644
--- a/src/sqitch.plan
+++ b/src/sqitch.plan
@@ -15,6 +15,8 @@ enum_event_visibility [schema_public] 1970-01-01T00:00:00Z Jonas Thelemann <e-ma
 table_notification [schema_private] 1970-01-01T00:00:00Z Jonas Thelemann <e-mail+maevsi/sqitch@jonas-thelemann.de> # Notifications that are sent via pg_notify.
 table_account_private [schema_private schema_public] 1970-01-01T00:00:00Z Jonas Thelemann <e-mail+maevsi/sqitch@jonas-thelemann.de> # Add private table account.
 table_account_public [schema_public schema_private table_account_private] 1970-01-01T00:00:00Z Jonas Thelemann <e-mail+maevsi/sqitch@jonas-thelemann.de> # Add public table account.
+table_account_block [schema_public table_account_public] 1970-01-01T00:00:00Z Sven Thelemann <sven.thelemann@t-online.de> # Blocking of an account by another account.
+table_account_block_policy [schema_public table_account_block role_account] 1970-01-01T00:00:00Z Sven Thelemann <sven.thelemann@t-online.de> # Policy for table account block.
 table_event_group [schema_public role_account role_anonymous table_account_public enum_event_visibility] 1970-01-01T00:00:00Z Jonas Thelemann <e-mail+maevsi/sqitch@jonas-thelemann.de> # Add table event_group.
 index_event_group_author_username [table_event_group] 1970-01-01T00:00:00Z Jonas Thelemann <e-mail+maevsi/sqitch@jonas-thelemann.de> # Add an index to the event group table's author_username field.
 table_event [schema_public role_account role_anonymous table_account_public] 1970-01-01T00:00:00Z Jonas Thelemann <e-mail+maevsi/sqitch@jonas-thelemann.de> # Add table event.
diff --git a/src/verify/table_account_block.sql b/src/verify/table_account_block.sql
new file mode 100644
index 0000000..378bac1
--- /dev/null
+++ b/src/verify/table_account_block.sql
@@ -0,0 +1,12 @@
+
+-- Verify maevsi:table_account_block on pg
+
+BEGIN;
+
+SELECT id,
+       author_account_id,
+       blocked_account_id,
+       created_at
+FROM maevsi.account_block WHERE FALSE;
+
+ROLLBACK;
diff --git a/src/verify/table_account_block_policy.sql b/src/verify/table_account_block_policy.sql
new file mode 100644
index 0000000..6d0d9e1
--- /dev/null
+++ b/src/verify/table_account_block_policy.sql
@@ -0,0 +1,21 @@
+-- Verify maevsi:table_account_block_policy on pg
+
+BEGIN;
+
+DO $$
+BEGIN
+  ASSERT (SELECT pg_catalog.has_table_privilege('maevsi_account', 'maevsi.account_block', 'INSERT'));
+  ASSERT (SELECT pg_catalog.has_table_privilege('maevsi_account', 'maevsi.account_block', 'SELECT'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_account', 'maevsi.account_block', 'UPDATE'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_account', 'maevsi.account_block', 'DELETE'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_anonymous', 'maevsi.account_block', 'SELECT'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_anonymous', 'maevsi.account_block', 'INSERT'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_anonymous', 'maevsi.account_block', 'UPDATE'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_anonymous', 'maevsi.account_block', 'DELETE'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_tusd', 'maevsi.account_block', 'SELECT'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_tusd', 'maevsi.account_block', 'INSERT'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_tusd', 'maevsi.account_block', 'UPDATE'));
+  ASSERT NOT (SELECT pg_catalog.has_table_privilege('maevsi_tusd', 'maevsi.account_block', 'DELETE'));
+END $$;
+
+ROLLBACK;