In the past 3 decades, the concept of professional community has gained considerable momentum in the theoretical and empirical studies in this field. At the same time, the concept has faced conceptual and methodological difficulties in that as yet no universal definition has been formulated and that its operationalization differs in the various empirical studies conducted on the subject. This study presents a comprehensive synthesis of the theories currently available and their implications for the conceptualization and operationalization of the professional community concept including a meta-analysis of the studies that investigated the effect of professional community on student achievement. Our meta-analysis reported a small but significant summary effect (d = 0.25, p less than 0.05), indicating that within a school environment professional community could enhance student achievement. Furthermore, the need for the conceptual and empirical validation of the concept's key dimension was discussed. (Contains 1 figure, 5 tables and 4 notes.)