This document provides a method overview, practice and use description, and language reference for the Integration Definition (IDEF) method for Process Description Capture (IDEF3). IDEF3 is designed to help document and analyze the processes of an existing or proposed system. Proven guidelines and a language for information capture help users capture and organize process information for multiple downstream uses. IDEF3 supports both process-centered and object-centered knowledge acquisition strategies enabling users to capture assertions about real-world processes and events in ways paralleling common forms of human expression. IDEF3 includes the ability to capture and structure descriptions of how a system works from multiple viewpoints. As an integral member of the IDEF family of methods, IDEF3 works well in independent application or in concert with other IDEF methods to document, analyze, and improve the vital processes of a business.