CoinJoin

CoinJoin is a privacy technique for Bitcoin that lets multiple users combine their transactions into one, making it difficult to figure out who owns which coins. Each participant contributes inputs and receives back outputs of the same size, so blockchain observers can’t easily link where specific coins ended up. This process breaks common tracking methods used in blockchain analysis.

Unlike traditional mixing services, with CoinJoin, no third party ever controls your funds—users retain control of their bitcoin throughout. To perform a CoinJoin, people coordinate to pool their coins, create a single large transaction with matching output amounts, and then each gets back their share. For example, if five users each want to send 1 BTC, they all contribute 1 BTC each and receive 1 BTC back, with no one able to tell whose is whose.

You can see a real CoinJoin transaction on the blockchain here.