Leadership is a conceptually ambiguous term, which creates a challenge for the practice of leadership development: How do we develop something without knowing what that “something” means? Prior research has not explored this challenge, and its existence has not stopped organizations from spending billions of dollars a year on leadership development. In this dissertation, I start by asking how individual leadership development programs can function in light of leadership’s ambiguity. I use qualitative theory-building methods in study 1 to generate an explanation for this question that is grounded in the concept of strategic ambiguity. In study 2, I followed up on one of the key implications of this explanation—potential competing incentives between science and practice—and asked how the science and practice of leadership development (mis)aligns. For this study, I used inductive coding on two sources: academic recommendations drawn from leadership development and leader behavior articles, and practitioner claims drawn from client/customer-facing websites. In the closing chapter, I develop big picture implications and questions for the science and practice of leadership and its development.