Succession planning has become increasingly important because of the shortage of headship applicants in England, and in many other countries. Leadership development is a central part of any succession planning strategy. This article compares the findings from two longitudinal studies, in England and South Africa, where the governments are seeking to improve the supply and quality of school principals, and links them to the literature. The article concludes that ensuring a good supply of able principals requires a proactive approach and should not be left to chance. (Contains 1 table and 3 notes.)