Over the years, most states and districts have focused professional development on teachers rather than principals. However, evidence suggests that principals can play an important role in reaching our national goals of high achievement for all students. School leaders are powerful levers for change--when given the right training and support. But most of the nation's school principals do not have access to professional learning that reflects what is happening in schools today (e.g., changing demographics, large-scale reform initiatives, changing technology, evolving instructional strategies) and what we know are effective practices. Improving principal professional development is going to require a new way of thinking, prioritizing, and budgeting--at the state and local levels. For example, professional learning for school staff tends to be a small part of school districts' budgets. And when funds are ample, districts overwhelmingly support teachers' professional development (Manna, 2015). But there are avenues for improving principal professional development. Some states and districts are already doing this work, and there is research that illustrates what can be done to enhance on-the-job principal professional development. This brief describes: (1) The need for more and better principal professional development to improve principal effectiveness, decrease principal turnover, and more equitably distribute successful principals across all schools; (2) The research on the importance of principals and how professional development can improve principals' effectiveness; and (3) Options and examples for leveraging current policies to revisit and refocus efforts concerning principal professional development.