What is the name of Telegram's messaging protocol?

Telegram's messaging protocol is MTProto. The name refers to the protocol Telegram developed to handle communication between its clients and servers, including message delivery, authentication, and data transport.

MTProto was created by Nikolai Durov and became a defining part of Telegram's technical architecture. It is distinct from better-known messaging protocols such as XMPP, which is an extensible communications standard, and Signal Protocol, which is used by apps including Signal and WhatsApp for end-to-end encryption.

A common mix-up is treating MTProto as though every Telegram conversation is automatically end-to-end encrypted. In ordinary cloud chats, messages are encrypted between the client and Telegram's servers and can be synchronized across devices. Secret Chats use end-to-end encryption and rely on a different security model. Telegram later replaced MTProto 1.0 with MTProto 2.0, which was deployed in 2017.