How do practicing mathematics teachers continue to develop the knowledge and habits of mind that enable them to teach well and to improve their teaching over time? This article reviews 106 articles written between 1985 and 2008 related to the professional learning of practicing teachers of mathematics. The authors offer a synthesis of this research, guided by Clarke and Hollingsworth’s (2002) dynamic model of teacher growth. Their model emphasizes the recursive nature of teachers’ learning and suggests that growth in one aspect of teachers’ knowledge and practice may promote subsequent growth in other areas.