Too often, software developers follow inefficient methods and procedures. The Personal Software Process, developed by Watts Humphrey at the Software Engineering Institute, provides software engineers with a methodology for consistently and efficiently developing high quality products. The value of PSP has been shown in three case studies-three industrial software groups have used PSP and have collected data to show its effectiveness. They are: Advanced Information Services, Inc., Motorola Paging Products Group, and Union Switch and Signal Inc. Each has trained several groups of engineers and measured the results of several projects that used PSP methods. In all cases, the projects were part of the companies' normal operations and not designed for this study. The three companies offered a variety of situations useful for demonstrating the versatility of PSP. The projects at Motorola and US&S involved software maintenance and enhancement, while those at AIS involved new product development and enhancement. Among the companies, application areas included commercial data processing, internal manufacturing support, communications product support, and real time process control. Work was done in C or C++.