Successful principals shape the culture of schools, set clear expectations, and share leadership with others to create productive learning environments for students and staff. For nearly a decade, The Wallace Foundation has coordinated studies of principal effectiveness and has concluded that principals are second only to teachers as the most influential school-based factor in student achievement. As states, districts, and schools strive to prepare all students for college and careers through full implementation of Common Core State Standards, transformed instruction, and new assessments, attention to the significant role of principals in this work is long overdue. Many report feeling overlooked in the Common Core movement and unprepared to guide teachers in implementation of the standards (Gewertz, 2012). Focused attention on the specific principal practices that support student achievement, transformation in instruction, and implementation of new standards will be a welcome relief to principals. The Wallace Foundation research identified five essential principal practices associated with increasing student achievement: (1) Shaping a vision of academic success for all students, one based in high standards; (2) Creating a climate hospitable to education in order that safety, a cooperative spirit, and other foundations for fruitful interaction prevail; (3) Cultivating leadership in others so that teachers and other adults assume their part in realizing the school vision; (4) Improving instruction to enable teacher to teach at their best and students to learn at their utmost; and (5) Managing people, data, and processes to foster school improvement. This brief, drawn from research and first-hand experiences of principals in schools across the country, examines specific practices in each category listed above that are likely to support implementation of Common Core standards and parallel, necessary changes. It also suggests how states, districts, and principals themselves can contribute to strengthening principal leadership for full implementation of Common Core State Standards.