A RESTful API is an application programming interface that adheres to Representational State Transfer (REST) principles, offering a standardized method to design web APIs using common web technologies. RESTful APIs are favored for web and mobile applications due to their simplicity, scalability, and ability to work across diverse platforms. They utilize standard HTTP methods such as GET, POST, PUT, and DELETE to manage resources, which can be represented in formats like JSON or XML. The stateless nature of RESTful interactions, where each request is independent, enhances efficiency and reliability. RESTful APIs also support caching to improve performance and are designed to be self-documenting for ease of use. Although REST is often contrasted with SOAP, REST’s lightweight, flexible architecture makes it a popular choice for modern applications connecting to microservices. It is compatible with many programming languages and platforms, and it incorporates authentication and security practices like API keys and OAuth 2.0 to ensure safe access to resources. RESTful API design emphasizes a uniform interface, statelessness, cacheability, and a layered system architecture for scalability and robustness.