This paper considers the nature of the Principal Assessment Center (PAC) innovation, discusses probable reasons for its popularity, and offers a few reflections on some implications of the success of this innovation. The first section considers the origin and nature of principal assessment centers and describes the model used by the Educational Leadership Center. The second section explores some of the possible reasons for the popularity of PACs. In the third and final section, the implications of sponsoring an innovation that may be "addictive" are considered. Appended is a table on skill dimensions considered in the PAC and 22 references. (Author/SI)