Chapter 6 introduces the mechanisms used by libraries and other information agencies to provide subject access, the processes by which we assist the user to identify information resources that contain information about a particular subject. This has traditionally involved deciding what the information resource is about, translating that into terms (words and phrases) or symbols which represent the subject, and providing access to terms and symbols through the library information retrieval system. In this chapter this process is outlined, key concepts relating to subject access are defined, and some key characteristics of indexing languages are noted.