RESTful APIs, or Representational State Transfer APIs, are a set of rules that allow different software applications to communicate over the internet. They use standard HTTP methods like GET, POST, PUT, and DELETE to perform operations on resources, which are typically represented in formats like JSON or XML. This architecture promotes scalability and simplicity, making it easier for developers to create and maintain web services. By adhering to REST principles, APIs can be stateless, meaning each request from a client contains all the information needed to process it. This leads to improved performance and reliability, as servers do not need to store session information. RESTful APIs are widely used in modern web applications, enabling seamless integration between different systems.