diff --git a/Cargo.lock b/Cargo.lock
index 14fdcdd69fe..b7407c89e2e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3554,7 +3554,7 @@ dependencies = [
  "solana-sdk",
  "solana-stake-program",
  "solana-vote-program",
- "spl-memo 2.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "spl-memo 2.0.1",
  "spl-token 3.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "thiserror",
 ]
@@ -3712,17 +3712,20 @@ dependencies = [
 [[package]]
 name = "spl-memo"
 version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fb2b771f6146dec14ef5fbf498f9374652c54badc3befc8c40c1d426dd45d720"
 dependencies = [
  "solana-program",
 ]
 
 [[package]]
 name = "spl-memo"
-version = "2.0.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fb2b771f6146dec14ef5fbf498f9374652c54badc3befc8c40c1d426dd45d720"
+version = "3.0.0"
 dependencies = [
  "solana-program",
+ "solana-program-test",
+ "solana-sdk",
+ "tokio 0.3.6",
 ]
 
 [[package]]
@@ -4062,7 +4065,7 @@ name = "test-client"
 version = "0.1.0"
 dependencies = [
  "solana-sdk",
- "spl-memo 2.0.1",
+ "spl-memo 3.0.0",
  "spl-token 3.0.1",
  "spl-token-swap",
 ]
diff --git a/docs/src/memo.md b/docs/src/memo.md
index 292831a6e38..d2098e8705c 100644
--- a/docs/src/memo.md
+++ b/docs/src/memo.md
@@ -2,9 +2,12 @@
 title: Memo Program
 ---
 
-A simple program that validates a string of UTF-8 encoded characters. It can be
-used to record a string on-chain, stored in the instruction data of a successful
-transaction.
+The Memo program is a simple program that validates a string of UTF-8 encoded
+characters and verifies that any accounts provided are signers of the
+transaction. The program also logs the memo, as well as any verified signer
+addresses, to the transaction log, so that anyone can easily observe memos and
+know they were approved by zero or more addresses by inspecting the transaction
+log from a trusted provider.
 
 ## Background
 
@@ -22,9 +25,54 @@ The Memo Program's source is available on
 ## Interface
 
 The on-chain Memo Program is written in Rust and available on crates.io as
-[spl-memo](https://crates.io/crates/spl-memo).
+[spl-memo](https://crates.io/crates/spl-memo) and
+[docs.rs](https://docs.rs/spl-memo).
 
-## Operational overview
+The crate provides a `build_memo()` method to easily create a properly
+constructed Instruction.
 
-The Memo program attempts to UTF-8 decode the instruction data; if successfully
-decoded, the instruction is successful.
+## Operational Notes
+
+If zero accounts are provided to the signed-memo instruction, the program
+succeeds when the memo is valid UTF-8, and logs the memo to the transaction log.
+
+If one or more accounts are provided to the signed-memo instruction, all must be
+valid signers of the transaction for the instruction to succeed.
+
+### Logs
+
+This section details expected log output for memo instructions.
+
+Logging begins with entry into the program:
+`Program MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr invoke [1]`
+
+The program will include a separate log for each verified signer:
+`Program log: Signed by <BASE_58_ADDRESS>`
+
+Then the program logs the memo length and UTF-8 text:
+`Program log: Memo (len 4): "🐆"`
+
+If UTF-8 parsing fails, the program will log the failure point:
+`Program log: Invalid UTF-8, from byte 4`
+
+Logging ends with the status of the instruction, one of:
+`Program MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr success`
+`Program MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr failed: missing required signature for instruction`
+`Program MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr failed: invalid instruction data`
+
+For more information about exposing program logs on a node, head to the
+[developer
+docs](https://docs.solana.com/developing/deployed-programs/debugging#logging)
+
+### Compute Limits
+
+Like all programs, the Memo Program is subject to the cluster's [compute
+budget](https://docs.solana.com/developing/programming-model/runtime#compute-budget).
+In Memo, compute is used for parsing UTF-8, verifying signers, and logging,
+limiting the memo length and number of signers that can be processed
+successfully in a single instruction. The longer or more complex the UTF-8 memo,
+the fewer signers can be supported, and vice versa.
+
+As of v1.5.1, an unsigned instruction can support single-byte UTF-8 of up to 566
+bytes. An instruction with a simple memo of 32 bytes can support up to 12
+signers.
diff --git a/memo/README.md b/memo/README.md
index 73744f63c6e..1cff1b99999 100644
--- a/memo/README.md
+++ b/memo/README.md
@@ -1,7 +1,9 @@
 # Memo Program
 
-A simple program that validates a string of UTF-8 encoded characters.  It can be
-used to record a string on-chain, stored in the instruction data of a successful
-transaction.
+A simple program that validates a string of UTF-8 encoded characters and logs it
+in the transaction log. The program also verifies that any accounts provided are
+signers of the transaction, and if so, logs their addresses. It can be used to
+record a string on-chain, stored in the instruction data of a successful
+transaction, and optionally verify the originator.
 
 Full documentation is available at https://spl.solana.com/memo
diff --git a/memo/program/Cargo.toml b/memo/program/Cargo.toml
index 9cfcd28cbf8..8657cc40b1e 100644
--- a/memo/program/Cargo.toml
+++ b/memo/program/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "spl-memo"
-version = "2.0.1"
+version = "3.0.0"
 description = "Solana Program Library Memo"
 authors = ["Solana Maintainers <maintainers@solana.foundation>"]
 repository = "https://github.com/solana-labs/solana-program-library"
@@ -9,10 +9,16 @@ edition = "2018"
 
 [features]
 no-entrypoint = []
+test-bpf = []
 
 [dependencies]
 solana-program = "1.5.1"
 
+[dev-dependencies]
+solana-program-test = "1.5.1"
+solana-sdk = "1.5.1"
+tokio = { version = "0.3", features = ["macros"]}
+
 [lib]
 crate-type = ["cdylib", "lib"]
 
diff --git a/memo/program/program-id.md b/memo/program/program-id.md
index bda1618a607..284ff6d8137 100644
--- a/memo/program/program-id.md
+++ b/memo/program/program-id.md
@@ -1 +1 @@
-Memo1UhkJRfHyvLMcVucJwxXeuD728EqVDDwQDxFMNo
+MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr
diff --git a/memo/program/run-tests.sh b/memo/program/run-tests.sh
new file mode 100755
index 00000000000..802b1ee53c2
--- /dev/null
+++ b/memo/program/run-tests.sh
@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+set -ex
+cd "$(dirname "$0")"
+cargo fmt -- --check
+cargo clippy
+cargo build
+cargo build-bpf
+
+if [[ $1 = -v ]]; then
+  export RUST_LOG=solana=debug
+fi
+
+cargo test
+cargo test-bpf
diff --git a/memo/program/src/entrypoint.rs b/memo/program/src/entrypoint.rs
index 0852451b548..82641a41587 100644
--- a/memo/program/src/entrypoint.rs
+++ b/memo/program/src/entrypoint.rs
@@ -1,43 +1,16 @@
 //! Program entrypoint
 
+#![cfg(not(feature = "no-entrypoint"))]
+
 use solana_program::{
-    account_info::AccountInfo, entrypoint, entrypoint::ProgramResult, program_error::ProgramError,
-    pubkey::Pubkey,
+    account_info::AccountInfo, entrypoint, entrypoint::ProgramResult, pubkey::Pubkey,
 };
-use std::str::from_utf8;
 
 entrypoint!(process_instruction);
 fn process_instruction(
-    _program_id: &Pubkey,
-    _accounts: &[AccountInfo],
+    program_id: &Pubkey,
+    accounts: &[AccountInfo],
     instruction_data: &[u8],
 ) -> ProgramResult {
-    from_utf8(instruction_data).map_err(|_| ProgramError::InvalidInstructionData)?;
-    Ok(())
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use solana_program::{program_error::ProgramError, pubkey::Pubkey};
-
-    #[test]
-    fn test_utf8_memo() {
-        let program_id = Pubkey::new(&[0; 32]);
-
-        let string = b"letters and such";
-        assert_eq!(Ok(()), process_instruction(&program_id, &[], string));
-
-        let emoji = "🐆".as_bytes();
-        let bytes = [0xF0, 0x9F, 0x90, 0x86];
-        assert_eq!(emoji, bytes);
-        assert_eq!(Ok(()), process_instruction(&program_id, &[], &emoji));
-
-        let mut bad_utf8 = bytes;
-        bad_utf8[3] = 0xFF; // Invalid UTF-8 byte
-        assert_eq!(
-            Err(ProgramError::InvalidInstructionData),
-            process_instruction(&program_id, &[], &bad_utf8)
-        );
-    }
+    crate::processor::process_instruction(program_id, accounts, instruction_data)
 }
diff --git a/memo/program/src/lib.rs b/memo/program/src/lib.rs
index ba495f0e97a..4f3b5d294e5 100644
--- a/memo/program/src/lib.rs
+++ b/memo/program/src/lib.rs
@@ -1,11 +1,34 @@
 #![deny(missing_docs)]
 
-//! A simple program that accepts a string of encoded characters and verifies that it parses. Currently handles UTF-8.
+//! A program that accepts a string of encoded characters and verifies that it parses,
+//! while verifying and logging signers. Currently handles UTF-8 characters.
 
-#[cfg(not(feature = "no-entrypoint"))]
 mod entrypoint;
+pub mod processor;
 
 // Export current sdk types for downstream users building with a different sdk version
 pub use solana_program;
+use solana_program::{
+    instruction::{AccountMeta, Instruction},
+    pubkey::Pubkey,
+};
 
-solana_program::declare_id!("Memo1UhkJRfHyvLMcVucJwxXeuD728EqVDDwQDxFMNo");
+solana_program::declare_id!("MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr");
+
+/// Build a memo instruction, possibly signed
+///
+/// Accounts expected by this instruction:
+///
+///   0. ..0+N. `[signer]` Expected signers; if zero provided, instruction will be processed as a
+///     normal, unsigned spl-memo
+///
+pub fn build_memo(memo: &[u8], signer_pubkeys: &[&Pubkey]) -> Instruction {
+    Instruction {
+        program_id: id(),
+        accounts: signer_pubkeys
+            .iter()
+            .map(|&pubkey| AccountMeta::new_readonly(*pubkey, true))
+            .collect(),
+        data: memo.to_vec(),
+    }
+}
diff --git a/memo/program/src/processor.rs b/memo/program/src/processor.rs
new file mode 100644
index 00000000000..f1cb19d95c1
--- /dev/null
+++ b/memo/program/src/processor.rs
@@ -0,0 +1,109 @@
+//! Program state processor
+
+use solana_program::{
+    account_info::AccountInfo, entrypoint::ProgramResult, msg, program_error::ProgramError,
+    pubkey::Pubkey,
+};
+use std::str::from_utf8;
+
+/// Instruction processor
+pub fn process_instruction(
+    _program_id: &Pubkey,
+    accounts: &[AccountInfo],
+    input: &[u8],
+) -> ProgramResult {
+    let account_info_iter = &mut accounts.iter();
+    let mut missing_required_signature = false;
+    for account_info in account_info_iter {
+        if let Some(address) = account_info.signer_key() {
+            msg!("Signed by {:?}", address);
+        } else {
+            missing_required_signature = true;
+        }
+    }
+    if missing_required_signature {
+        return Err(ProgramError::MissingRequiredSignature);
+    }
+
+    let memo = from_utf8(input).map_err(|err| {
+        msg!("Invalid UTF-8, from byte {}", err.valid_up_to());
+        ProgramError::InvalidInstructionData
+    })?;
+    msg!("Memo (len {}): {:?}", memo.len(), memo);
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use solana_program::{
+        account_info::IntoAccountInfo, program_error::ProgramError, pubkey::Pubkey,
+    };
+    use solana_sdk::account::Account;
+
+    #[test]
+    fn test_utf8_memo() {
+        let program_id = Pubkey::new(&[0; 32]);
+
+        let string = b"letters and such";
+        assert_eq!(Ok(()), process_instruction(&program_id, &[], string));
+
+        let emoji = "🐆".as_bytes();
+        let bytes = [0xF0, 0x9F, 0x90, 0x86];
+        assert_eq!(emoji, bytes);
+        assert_eq!(Ok(()), process_instruction(&program_id, &[], &emoji));
+
+        let mut bad_utf8 = bytes;
+        bad_utf8[3] = 0xFF; // Invalid UTF-8 byte
+        assert_eq!(
+            Err(ProgramError::InvalidInstructionData),
+            process_instruction(&program_id, &[], &bad_utf8)
+        );
+    }
+
+    #[test]
+    fn test_signers() {
+        let program_id = Pubkey::new(&[0; 32]);
+        let memo = "🐆".as_bytes();
+
+        let pubkey0 = Pubkey::new_unique();
+        let pubkey1 = Pubkey::new_unique();
+        let pubkey2 = Pubkey::new_unique();
+        let mut account0 = Account::default();
+        let mut account1 = Account::default();
+        let mut account2 = Account::default();
+
+        let signed_account_infos = vec![
+            (&pubkey0, true, &mut account0).into_account_info(),
+            (&pubkey1, true, &mut account1).into_account_info(),
+            (&pubkey2, true, &mut account2).into_account_info(),
+        ];
+        assert_eq!(
+            Ok(()),
+            process_instruction(&program_id, &signed_account_infos, memo)
+        );
+
+        assert_eq!(Ok(()), process_instruction(&program_id, &[], memo));
+
+        let unsigned_account_infos = vec![
+            (&pubkey0, false, &mut account0).into_account_info(),
+            (&pubkey1, false, &mut account1).into_account_info(),
+            (&pubkey2, false, &mut account2).into_account_info(),
+        ];
+        assert_eq!(
+            Err(ProgramError::MissingRequiredSignature),
+            process_instruction(&program_id, &unsigned_account_infos, memo)
+        );
+
+        let partially_signed_account_infos = vec![
+            (&pubkey0, true, &mut account0).into_account_info(),
+            (&pubkey1, false, &mut account1).into_account_info(),
+            (&pubkey2, true, &mut account2).into_account_info(),
+        ];
+        assert_eq!(
+            Err(ProgramError::MissingRequiredSignature),
+            process_instruction(&program_id, &partially_signed_account_infos, memo)
+        );
+    }
+}
diff --git a/memo/program/tests/functional.rs b/memo/program/tests/functional.rs
new file mode 100644
index 00000000000..41f917d5f40
--- /dev/null
+++ b/memo/program/tests/functional.rs
@@ -0,0 +1,207 @@
+#![cfg(feature = "test-bpf")]
+
+use solana_program::{
+    instruction::{AccountMeta, Instruction, InstructionError},
+    pubkey::Pubkey,
+};
+use solana_program_test::*;
+use solana_sdk::{
+    signature::{Keypair, Signer},
+    transaction::{Transaction, TransactionError},
+};
+use spl_memo::*;
+
+fn program_test() -> ProgramTest {
+    ProgramTest::new("spl_memo", id(), processor!(processor::process_instruction))
+}
+
+#[tokio::test]
+async fn test_memo_signing() {
+    let memo = "🐆".as_bytes();
+    let (mut banks_client, payer, recent_blockhash) = program_test().start().await;
+
+    let keypairs = vec![Keypair::new(), Keypair::new(), Keypair::new()];
+    let pubkeys: Vec<Pubkey> = keypairs.iter().map(|keypair| keypair.pubkey()).collect();
+
+    // Test complete signing
+    let signer_key_refs: Vec<&Pubkey> = pubkeys.iter().collect();
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(memo, &signer_key_refs)], Some(&payer.pubkey()));
+    let mut signers = vec![&payer];
+    for keypair in keypairs.iter() {
+        signers.push(keypair);
+    }
+    transaction.sign(&signers, recent_blockhash);
+    banks_client.process_transaction(transaction).await.unwrap();
+
+    // Test unsigned memo
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(memo, &[])], Some(&payer.pubkey()));
+    transaction.sign(&[&payer], recent_blockhash);
+    banks_client.process_transaction(transaction).await.unwrap();
+
+    // Demonstrate success on signature provided, regardless of specific memo AccountMeta
+    let mut transaction = Transaction::new_with_payer(
+        &[Instruction {
+            program_id: id(),
+            accounts: vec![
+                AccountMeta::new_readonly(keypairs[0].pubkey(), true),
+                AccountMeta::new_readonly(keypairs[1].pubkey(), true),
+                AccountMeta::new_readonly(payer.pubkey(), false),
+            ],
+            data: memo.to_vec(),
+        }],
+        Some(&payer.pubkey()),
+    );
+    transaction.sign(&[&payer, &keypairs[0], &keypairs[1]], recent_blockhash);
+    banks_client.process_transaction(transaction).await.unwrap();
+
+    // Test missing signer(s)
+    let mut transaction = Transaction::new_with_payer(
+        &[Instruction {
+            program_id: id(),
+            accounts: vec![
+                AccountMeta::new_readonly(keypairs[0].pubkey(), true),
+                AccountMeta::new_readonly(keypairs[1].pubkey(), false),
+                AccountMeta::new_readonly(keypairs[2].pubkey(), true),
+            ],
+            data: memo.to_vec(),
+        }],
+        Some(&payer.pubkey()),
+    );
+    transaction.sign(&[&payer, &keypairs[0], &keypairs[2]], recent_blockhash);
+    assert_eq!(
+        banks_client
+            .process_transaction(transaction)
+            .await
+            .unwrap_err()
+            .unwrap(),
+        TransactionError::InstructionError(0, InstructionError::MissingRequiredSignature)
+    );
+
+    let mut transaction = Transaction::new_with_payer(
+        &[Instruction {
+            program_id: id(),
+            accounts: vec![
+                AccountMeta::new_readonly(keypairs[0].pubkey(), false),
+                AccountMeta::new_readonly(keypairs[1].pubkey(), false),
+                AccountMeta::new_readonly(keypairs[2].pubkey(), false),
+            ],
+            data: memo.to_vec(),
+        }],
+        Some(&payer.pubkey()),
+    );
+    transaction.sign(&[&payer], recent_blockhash);
+    assert_eq!(
+        banks_client
+            .process_transaction(transaction)
+            .await
+            .unwrap_err()
+            .unwrap(),
+        TransactionError::InstructionError(0, InstructionError::MissingRequiredSignature)
+    );
+
+    // Test invalid utf-8; demonstrate log
+    let invalid_utf8 = [0xF0, 0x9F, 0x90, 0x86, 0xF0, 0x9F, 0xFF, 0x86];
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(&invalid_utf8, &[])], Some(&payer.pubkey()));
+    transaction.sign(&[&payer], recent_blockhash);
+    assert_eq!(
+        banks_client
+            .process_transaction(transaction)
+            .await
+            .unwrap_err()
+            .unwrap(),
+        TransactionError::InstructionError(0, InstructionError::InvalidInstructionData)
+    );
+}
+
+#[tokio::test]
+async fn test_memo_compute_limits() {
+    let (mut banks_client, payer, recent_blockhash) = program_test().start().await;
+
+    // Test memo length
+    let mut memo = vec![];
+    for _ in 0..1000 {
+        let mut vec = vec![0x53, 0x4F, 0x4C];
+        memo.append(&mut vec);
+    }
+
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(&memo[..566], &[])], Some(&payer.pubkey()));
+    transaction.sign(&[&payer], recent_blockhash);
+    banks_client.process_transaction(transaction).await.unwrap();
+
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(&memo[..567], &[])], Some(&payer.pubkey()));
+    transaction.sign(&[&payer], recent_blockhash);
+    assert_eq!(
+        banks_client
+            .process_transaction(transaction)
+            .await
+            .unwrap_err()
+            .unwrap(),
+        TransactionError::InstructionError(0, InstructionError::ProgramFailedToComplete)
+    );
+
+    let mut memo = vec![];
+    for _ in 0..100 {
+        let mut vec = vec![0xE2, 0x97, 0x8E];
+        memo.append(&mut vec);
+    }
+
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(&memo[..60], &[])], Some(&payer.pubkey()));
+    transaction.sign(&[&payer], recent_blockhash);
+    banks_client.process_transaction(transaction).await.unwrap();
+
+    let mut transaction =
+        Transaction::new_with_payer(&[build_memo(&memo[..63], &[])], Some(&payer.pubkey()));
+    transaction.sign(&[&payer], recent_blockhash);
+    assert_eq!(
+        banks_client
+            .process_transaction(transaction)
+            .await
+            .unwrap_err()
+            .unwrap(),
+        TransactionError::InstructionError(0, InstructionError::ProgramFailedToComplete)
+    );
+
+    // Test num signers with 32-byte memo
+    let memo = Pubkey::new_unique().to_bytes();
+    let mut keypairs = vec![];
+    for _ in 0..20 {
+        keypairs.push(Keypair::new());
+    }
+    let pubkeys: Vec<Pubkey> = keypairs.iter().map(|keypair| keypair.pubkey()).collect();
+    let signer_key_refs: Vec<&Pubkey> = pubkeys.iter().collect();
+
+    let mut signers = vec![&payer];
+    for keypair in keypairs[..12].iter() {
+        signers.push(keypair);
+    }
+    let mut transaction = Transaction::new_with_payer(
+        &[build_memo(&memo, &signer_key_refs[..12])],
+        Some(&payer.pubkey()),
+    );
+    transaction.sign(&signers, recent_blockhash);
+    banks_client.process_transaction(transaction).await.unwrap();
+
+    let mut signers = vec![&payer];
+    for keypair in keypairs[..13].iter() {
+        signers.push(keypair);
+    }
+    let mut transaction = Transaction::new_with_payer(
+        &[build_memo(&memo, &signer_key_refs[..13])],
+        Some(&payer.pubkey()),
+    );
+    transaction.sign(&signers, recent_blockhash);
+    assert_eq!(
+        banks_client
+            .process_transaction(transaction)
+            .await
+            .unwrap_err()
+            .unwrap(),
+        TransactionError::InstructionError(0, InstructionError::ProgramFailedToComplete)
+    );
+}