The most basic type of smart contract is a multi-signature smart contract. A multisig transaction states that a defined number of people (public keys) must sign a transaction with their private keys before it’s considered valid. Bitcoin was the first blockchain to introduce multisig transactions in 2012.
![A simple framework for a multisig transaction on the Bitcoin blockchain](https://blog.chain.link/content/images/2020/06/btc.png)