The Bluesky Social app is built on an open network protocol that refers to each user by a unique Decentralized Identifier, or DID (a W3C standard). The most popular supported DID method was developed in-house by Bluesky Social, and is called "Public Ledger of Credentials", or PLC. The PLC identity system currently relies on a global directory service to distribute identity updates, and that directory service has been operated by Bluesky as well.