This document discusses APIs and how they can be used to integrate different applications together. It defines what an API is and how APIs allow programs to interact with and extract data from other applications. It then outlines several common approaches for integrating systems together, including using direct API calls from one system to another, developing custom middleware that processes requests and responses between systems, or building logic into one of the integrated applications. The document emphasizes that APIs enable easy and cheap integration of data from various sources to create new applications and solutions without needing developers.