The document discusses API layers in Mule and their uses. An API layer offers a decoupled interface for interacting with applications through a common language-agnostic way. Common uses of API layers include connecting to legacy systems that lack REST APIs and publishing APIs for partners to communicate with systems. The Anypoint Platform helps build, design, and manage APIs to expose enterprise data securely to various devices and apps. It includes an API gateway to connect to backends behind firewalls, an API manager to manage users and traffic, an API contract manager to issue keys and monitor compliance, and an API policy manager to apply security policies without downtime.