Teacher educators, policy makers, and school administrators have long been concerned with new teachers' initial preparedness to teach. However, how to conceptualize and to validly measure teacher preparedness and the extent to which it is predictive of teacher retention are not entirely clear. This longitudinal study draws on data on hundreds of mathematics teachers to examine the relationship between their initial feelings of preparedness and their retention. The study finds that both math-specific and subject-general measures of mathematics teachers' feelings of initial preparedness predict their 5- and 8-year retention in first schools, their 8-year retention in the district that hired them, and their 8-year retention in the profession in general.