In computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behavior of a hardware connection.

Protocols should be distinguished from technical standards, which variously specify how to build a computer or related hardware device, or how the contents of a file are structured, or describe the static structure of a network interface. Protocols are generally used to define real-time communications behavior, while standards are used to govern the structure of information committed to long-term storage.