APIs, or application programming interfaces, facilitate communication between applications and systems, serving as access points to underlying data and functions. Different types of APIs can be categorized by their access types—open, partner, private, and public—or by their design patterns, including RPC, SOAP, REST, and GraphQL. Each design pattern offers unique advantages suited to particular use cases in software development, especially in SaaS integrations. RPC APIs, established in the late 1970s, are valued for their efficiency in data exchange using binary formats. SOAP APIs, developed in the late 1990s, are known for their structured, protocol-guided approach to secure data transmission. REST APIs, emerging in 2000, are favored for their simplicity and scalability, making them the most prevalent in web applications. GraphQL APIs, the newest design pattern, address limitations in REST by enabling more efficient data retrieval with a single request. The choice of API design pattern should align with the specific needs of the development project, as each offers distinct advantages and can be implemented effectively by experienced developers.