Software maintenance rep-resents the largest cost element in the life of a software system, and the process of understanding the software system utilizes 50 percent of the time spent on software maintenance. Thus there is a need for tools to aid the program understanding task. The tool described in this paper-ogram UNderstanding Support environment (PUNS)-ovides the needed environment. Here the program understanding task is supported with multiple views of the program and a simple strategy for moving between views and exploring a particular view in depth. PUNS consists of a repository component that loads and manages a repository of information about the program to be understood and a user interface component that presents the information in the repository, utilizing graphics to emphasize the relationships and allowing the user to move among the pieces of information quickly and easily.