Software evolution is required to keep a software system in sync with the ever-changing needs of the system's users and environment. An unfortunate side-effect of evolution is that it often causes the knowledge about a system to degrade, which in turn impedes further evolution.In the dissertation, we investigate techniques and tools that help remedy this situation by supporting the exploration of a software system and improving its legibility [1]. We examine the analogy with urban exploration and present innovative techniques for the extraction, abstraction, and presentation of information needed for understanding software.