This chapter summarizes what the best available nationally representative data reveal about the rates of, and reasons for, the turnover of math and science teachers. The results show that contrary to conventional wisdom, the problems schools have adequately staffing classrooms with qualified teachers are not due to increases in student enrollment or increases in teacher retirement. Rather, large numbers of teachers leave teaching for other reasons, such as job dissatisfaction and in order to pursue other careers. These findings suggest that educational policy initiatives will not solve school staffing problems if they do not address the problem of teacher retention. (Contains 12 references.) (Author/NB)