The NASA Personnel Security Processing Expert System is a tool that automatically determines the appropriate personnel background investigation required for a civil servant or contractor occupying a position of national security or public trust. It also instructs the personnel security processing staff to perform special checks based on a specific position. The system is implemented using a rule-based expert system and a World Wide Web interface. The system design separates the user interface, knowledge base and control structure to simplify system evolution. When one subsystem is modified, the others are impacted minimally. This system provides many benefits to the NASA Personnel Security Program. First, it frees the agency personnel security specialist from trouble-shooting and correcting all investigative problems. It also provides a learning tool for security processing staff at each installation. The system ensures that each installation security office is in compliance with all applicable laws, regulations and policies. Finally, eliminating overlapping, inappropriate and duplicative efforts to process employees saves many resources. The system was deployed less than a year ago. To date, it saved $1.2 million of the $1.5 million agency-wide personnel security budget.