Multisig — multi-signature — is a wallet configuration where spending requires more than one private key. The most common shape is 2-of-3: three keys exist, any two are required to sign, the third can be lost without losing the funds. The single largest custody upgrade available to a US holder past the six-figure threshold.
What 2-of-3 actually means
You hold three independent keys, typically on three different devices in three different locations. The receiving address is a special "multisig address" generated by combining all three public keys. To spend from it, the wallet collects signatures from any two of the three keys — the third can be a co-signer, an executor, a backup in cold storage, or simply destroyed.
The result is a wallet with no single point of failure. Lose one key and the funds are still recoverable. Lose one device entirely and the funds are still safe. Have one key compromised and the attacker still cannot spend.
Implementations a US holder will encounter
On-chain multisig (Bitcoin native). Sparrow Wallet, Specter, Bitcoin Core, Liana — all support n-of-m multisig with hardware-wallet co-signers. Transactions are visible on chain as multisig spends. This is the most battle-tested implementation; the protocol has supported it since 2012 via P2SH and since 2017 via SegWit.
Smart-contract multisig (Ethereum). Safe (formerly Gnosis Safe) is the dominant choice. Multisig logic runs in a smart contract; signatures are collected off-chain and submitted to the contract for execution. Used by most DAOs, all major DeFi protocols, and a growing number of US-resident high-net-worth individuals managing six and seven-figure positions.
Custodial multisig. Casa, Unchained Capital, and BitGo all offer "managed multisig" where the service holds one or two keys, you hold the rest. Useful for non-technical US holders with substantial stacks who want operational backup and inheritance services; less interesting to anyone willing to run Sparrow or Safe themselves.
The setup that actually works
A 2-of-3 multisig for a US-resident holder typically looks like: key 1 on a hardware wallet at home, key 2 on a hardware wallet at a CPA or attorney's office (or a bank safe-deposit box), key 3 in a sealed envelope at a trusted family member's home. Use three different hardware-wallet brands — Ledger plus Trezor plus Coldcard, say — to avoid single-vendor supply-chain risk.
The setup takes a weekend to do properly. Pair it with a written recovery document that explains to a non-technical executor how to coordinate two of the three keys without exposing the third. Without that document, the multisig is more dangerous than a single-key cold wallet.
When multisig is the wrong call
Under a $25K stack, the operational complexity exceeds the marginal security gain. Stick with single-sig hardware wallet plus a steel backup. Above $250K, multisig becomes the default.
Further reading: Shamir Backup, Hardware wallet, Social recovery wallet.