To work effectively with legacy code, software engineers need to understand a legacy computer program's culture - the combination of the programmer's background, the hardware environment and the programming techniques that guided its creation. Software systems typically pass through a series of stages. During the initial development stage, software developers create a first functioning version of the code. An evolution stage follows, during which developmental efforts focus on extending system capabilities to meet user needs. During the servicing stage, only minor repairs and simple functional changes are possible. In the phase-out stage, the system is essentially frozen, but it still produces value. Finally, during the close-down stage, the developers withdraw the system and possibly replace it. Most of the tasks in the evolution and servicing phases require program comprehension /sup n/derstanding how and why a software program functions in order to work with it effectively. Effective comprehension requires viewing a legacy program not simply as a product of inefficiency or stupidity, but instead as an artifact of the circumstances in which it was developed. This information can be an important factor in determining appropriate strategies for the software program's transition from the evolution stage to the servicing or phase-out stage.