Explore API design for evolving systems in this conference talk from GOTO Amsterdam 2019. Delve into the architectural context of APIs, examining the drawbacks of ignoring crucial REST principles. Investigate the distinction between internal and external APIs, and learn how Domain-Driven Design impacts API development. Discover strategies for designing and specifying APIs and their evolution without relying solely on versioning. Gain insights into topics such as hypermedia, state machines, API documentation, and the balance between domain knowledge and protocol knowledge. Through a sample application, understand how to create flexible, adaptable APIs that can evolve alongside interconnected systems.