During the past 10 to 15 years, nearly every state and school district across the nation has begun to dramatically overhaul their evaluation systems for teachers. Such evaluation systems are ultimately aimed at improving teachers' instructional practices. However, the evidence on the efficacy and effectiveness of these systems is weak and equivocal at best. One of the major factors associated with the lack of impact of these systems is the troublesome relationship between evaluation and professional development--the opportunities for teachers to learn and improve their practice in response to and beyond the process of evaluation itself. Policies governing teacher evaluation systems tend to make only vague and weak provisions for professional development, and they fail to ensure that these opportunities are of high quality and of value in improving practice. If states are to improve the effectiveness of their teacher evaluation systems, they should make the provision of high quality professional development to all teachers a key element of these systems. Without more attention to professional development as a key complement to evaluation, recently developed teacher evaluation systems will likely fail to improve teachers' practices in the ways theorized by their proponents. [This policy brief was originally published through the Research on Urban Education Policy Initiative at the University of Illinois at Chicago.]