Multisignature wallets guard most of the serious money in crypto: DAO treasuries, exchange cold storage, protocol funds, and the savings of the security-conscious. They are also at the center of the industry’s biggest heists, from Bybit’s $1.5 billion to this year’s UXLINK breach, because attackers stopped picking locks and started fooling the people holding the keys. This guide explains how multisig actually works, the M-of-N design choices, how the famous multisig hacks really happened, and how to run one without becoming a case study.