A Multi-Signature wallet (Multi-Sig) is a smart contract that requires multiple owners to approve transactions before they can be executed. Instead of one person controlling the funds with a single private key, the smart contract enforces that multiple people must sign off before any transaction goes through.

Modern multi-sigs like Gnosis Safe use off-chain signatures - owners sign messages without paying gas. Once enough signatures are collected, anyone can execute the transaction on-chain, with gas paid from the multi-sig balance.

The most common setup is a 3/4 multisig, where at least 3 out of 4 owners must sign to approve a transaction. Try it yourself in the demo: connect to the multi-sig contract, initiate a transaction, and watch how 3 different owner wallets need to approve before the smart contract executes it. Notice how the 4th owner doesn't need to sign - this flexibility means you don't lose access to funds if one owner loses their wallet.