Software professionals rely on internal documentation as an aid in understanding programs. Unfortunately, the documentation for most programs is usually out-of-date and cannot be trusted. Without it, the only reliable and objective information is the source code itself. Personnel must spend an inordinate amount of time exploring the system by looking at low-level source code to gain an understanding of its functionality. One way of producing accurate documentation for an existing software system is through reverse engineering. This paper outlines a reverse engineering methodology for building subsystem structures out of software building blocks, and describes how documenting a software system with views created by this process can produce numerous benefits. It addresses primarily the needs of the software engineer and technical manager as document users.