This document discusses SOAP and REST APIs. It defines an API as an interface that allows applications to communicate with each other by defining operations, inputs, outputs, and data types. APIs can be traditional server-to-server or web APIs, which are the focus. Web APIs exist in formats like SOAP, JSON-RPC, XML-RPC, and REST. SOAP APIs can communicate over different protocols but require SOAP libraries and rely on XML. REST APIs typically use HTTP and support various content types while being stateless and easier for developers. References are provided for sample SOAP and REST APIs that can be called from PL/SQL.