Effective school leaders significantly influence the performance of their schools. Unfortunately, in many countries worldwide attracting qualified candidates to become school principals is becoming increasingly difficult. This paper reports on several comparative studies that were carried out within the framework of a long-term research cooperation between a German and an US-American University. The aim of these studies was to clarify the motivation of teachers in deciding for or against taking over a position as a principal. For a better understanding of the background, the article also includes a section on the similarities and differences between the school systems of Germany and the USA and the responsibilities of principals.