At one time, finding an assistant principal for a public school in Denver entailed a search through "a gajillion résumés," in the words of one local school district administrator. Even then, some ideal candidates likely fell through the cracks. Those days are over, owing to the development by Denver Public Schools of a "leader tracking system," a database of information about the training, qualifications and performance of principals and aspiring principals. This Story From the Field examines how Denver and five other school districts have constructed and are using these systems as they seek to better train, hire and support school principals. All six districts are taking part in the Principal Pipeline Initiative, a Wallace Foundation-funded effort to help the school systems develop a large corps of strong school principals and generate lessons for the field. In addition to aiding district officials in identifying strong principal and assistant principal candidates and matching them to the right schools, the leader tracking systems are helping in efforts to forecast job vacancies, pinpoint principal training topics and spot potential principal mentors. The districts are also beginning to use the systems to share aggregate information about the performance of principals with the preparation programs from which the principals graduated. The publication makes clear that developing a leader tracking system takes time and effort. It describes, for example, how determining what information to collect, and then finding it, proved to be a key but time-consuming task, not least because essential data could be housed in different niches of the school bureaucracies.