This encyclopedia entry introduces the JSON (JavaScript Object Notation) format, the universal data exchange standard of modern computing. The description explains the history of the format and how it replaced earlier XML-based solutions with its simplicity and efficiency. We discuss in detail the strict yet understandable syntax of JSON and the supported data types. The article also covers important technological extensions based on JSON, such as JSON Schema for data validation, JSON-RPC for remote procedure calls, and JSON-LD, which forms the basis of the semantic web. A separate chapter deals with its role in the Linux environment, touching on configuration files, structured logging, and the jq command-line processing tool. Finally, we objectively consider the advantages of the format, such as language independence, and its disadvantages, such as the lack of comments.