What is Multisig (Multisignature)?
A security feature that requires multiple private keys to authorize a Bitcoin transaction. For example, a 2-of-3 multisig wallet requires any 2 out of 3 designated keys to sign a transaction.
Why It Matters
Multisig gives you security through redundancy. Take a 2-of-3 setup. You keep one key. A trusted family member holds the second. A safe deposit box holds the third. Three keys total. Any two can spend.
You can lose one key and still spend. A thief can steal one key and still not spend. Far more secure than single-key custody. Large institutions and family offices use multisig extensively. The structure scales: 3-of-5, 4-of-7, whatever the situation needs. Multisig transforms Bitcoin security from all-or-nothing into a graduated system where compromise of any single key is no longer sufficient to drain your wallet, which is exactly the property you want for any meaningful long-term holding.
How It Works
A multisig address is created from multiple public keys, specifying how many signatures are required. The format is "m-of-n." For example: 2-of-3 requires any 2 out of 3 private keys to sign transactions from that address.
When you want to spend multisig bitcoin, you create a transaction. It gets passed around for signing. Each required signer (at least 2 in our example) signs with their private key. Once enough signatures are collected, the transaction is complete. Broadcast. Done. Bitcoin's scripting language enforces the requirement at the protocol level. Nodes verify the proper number of signatures are present before accepting the transaction into a block.
A worked example. Casa offers a 2-of-3 multisig service for individual holders: one key on your phone, one key on a hardware device, one held by Casa as backup. Spending requires any 2 of the 3. Lose your phone, you still have the other two. A thief who steals your phone can't spend without one of the other two. Companies like BitGo and Unchained Capital offer similar setups for institutional holders managing hundreds of millions in bitcoin. Multisig is also baked into protocol upgrades like Taproot that make multisig signatures more efficient and indistinguishable from single-key signatures on the blockchain.