CoinJoin is a privacy method used in the Bitcoin network (and sometimes other cryptocurrencies) that allows multiple users to combine their transactions into a single one. By combining these transactions, CoinJoin makes it much more difficult for an external observer to trace the origin and destination of the funds, thereby improving the anonymity of users.

Contrary to popular belief, CoinJoin does not modify the Bitcoin protocol: it is a technique compatible with its native operation. It relies on voluntary collaboration among users who wish to protect their privacy without compromising the security or integrity of their funds.