REST (Representational State Transfer): An architectural style for APIs relying on stateless communication and standard HTTP methods. SOAP (Simple Object Access Protocol): A protocol-based API that uses XML for structured communication over HTTP or SMTP. GraphQL: A query language for APIs that allows clients to request specific data, reducing over-fetching. WebSocket: Enables real-time, full-duplex communication between a client and server over a single connection. gRPC (Google Remote Procedure