Common sense and recent research make it clear that schools cannot be successful without strong principals. Strong principals help improve student performance in many ways, from shaping a school's mission and culture to hiring, developing, and retaining its teachers. Even so, principals often get short shrift in today's debates about human capital in public education. Compared to the large body of research and policy attention given to teachers, the field knows surprisingly little about the principal workforce. This knowledge gap means that it often is hard for school districts and states to make strategic decisions to improve their principal workforces. Where do most principals come from? How long do they stay? How well do they perform? How many will need to be hired and developed in the future? Few districts or states know the answers. To address these and other important questions about their principals, states need, among other things, to build detailed longitudinal data systems like the ones they use to track teachers and students. But in some places those types of systems are still a long way off. In the meantime, system leaders can examine the administrative data they already have to paint a basic picture of their principal workforce, one that can help prompt deeper questions and discussions about the challenges and opportunities they face. This "Principal Concerns" brief offers an example of this type of analysis for Wisconsin. Why should Wisconsin be concerned about its principal workforce? After all, by some measures, the state's schools are doing well. Wisconsin's NAEP scores, for example, are consistently higher than the national average. Yet there is still much work to be done to ensure that all students achieve at high levels, and strong leadership is key to that success. Under the state's recently revamped accountability system, 266 schools across the state are not meeting performance expectations. In Milwaukee Public Schools, the state's largest school system, only 21 percent of schools met or exceeded the state's expectations. (Contains 3 figures and 11 footnotes.)