Principals are critical to the success of any school improvement effort--from increasing academic rigor toward college- and career-ready standards to teacher evaluation and support. They ensure this success by building a strong, shared vision and leading effective implementation for staff, students, and families. The federal government has an important role to play in supporting the development of leaders who are preparing students for success in college, careers, and citizenship. Investments in principals are the best long-term investment in effective implementation of other federal policy priorities. Smart federal policies champion the importance of principals, set the conditions for strong state and district policies, support innovative models and promising practices, promote accountability for results, and build on-the-ground capacity to support effective leadership. All smart principal policies--including those at the federal level--should be grounded in the actions of effective leaders. Principals are expected to meet an increasingly complex set of expectations. And the best principals do so by playing three critical roles: (1) Instructional Leader; (2) Talent Manager; and (3) Culture Builder. These crucial roles are supported by operations and systems that support learning and are enhance by a principal's personal leadership characteristics. In this five-part series, policymakers are encouraged to consider how various policies--as part of a comprehensive school leadership reform agenda--will impact a principal throughout her career. [For Brief 1, "A Shared Vision of Leadership," see ED559352. For Brief 2, "Pipeline Development," see ED559349. For Brief 3, "Pre-Service Preparation," see ED559355. For Brief 4, "Evaluation and Management," see ED559353. For Brief 5, "Retention and Rewards," see ED559350.]