Teacher evaluation systems that pair measures of teacher observation with measures of student achievement or growth have become widespread. However, little attention has focused on the impact of teacher evaluation systems--and, in particular, the intensive collection and use of data from teacher observations--on principals. Drawing on interviews with approximately 60 principals in 6 urban school districts, we describe how teacher observation policies are reshaping school leadership. Principals report spending time in new ways, citing benefits to teacher evaluation, such as collecting evidence about teacher performance to provide specific, evidence-based, formative feedback to teachers. They navigate new expectations around data use, particularly in the area of teacher "talent management," such as teacher support. These changes come with substantial challenges, including lack of time to complete duties, deterioration of relationships, and lower visibility in schools, raising the possibility that teacher evaluation systems may be increasing principal stress and burnout.