The implementation of "the Common Core Standards for Mathematics" and the assessments of those concepts, skills, reasoning methods, and mathematical practices that are in development necessitate the updating of teachers' knowledge of content, pedagogical techniques to enhance engagement and persistence, and strategies for responding to the needs and talents of students. Following a brief history of the role of supervisors, the key responsibilities of current supervisors are described and include strategies for: establishing a framework for instruction, collaborating with other content curriculum supervisors to explore ways to enhance key concept acquisition in two or more fields, identifying students' academic needs and monitoring their progress, designing and conducting ongoing PD programs, closing learning gaps, and celebrating achievements of both students and teachers. The chapter concludes with an identification of the qualifications and characteristics of effective supervisors of mathematics.