What makes a group of good citizens? The role of perceived group-level fit and critical psychological states in organizational teams Yuhyung Shin 1 * and Jin Nam Choi 2 1 College of Business Administration, Hanyang University, Seoul, Republic of Korea 2 College of Business Administration, Seoul National University, Republic of Korea Recent studies have expanded the construct of organizational citizenship behaviour (OCB) to the group level and demonstrated its significance in predicting group performance. In this study, we have further expanded this growing stream of research regarding group-level OCB (GOCB), by identifying distinct group characteristics that predict GOCB. Specifically, we have isolated perceived group–organization (G–O) fit and group–task (G–T) fit as meaningful antecedents of GOCB. We further propose that the perceived G–O and G–T fit influence GOCB by shaping two intermediate psychological states of group members: cohesion and group efficacy. Our findings, which were based on multi-source data collected from 43 organizational teams, demonstrated that cohesion completely mediated the effect of perceived G–O fit on GOCB. Group efficacy, however, proved not to be a significant mediator of the relationship between perceived G–T fit and GOCB. Instead, G–T fit had a significant direct effect on GOCB. This study highlights the significance of group-level conceptualization of group–environment interaction as a potential driver of various group processes and outcomes. With increasing competitive pressure obliging organizations to do more with less, the mobilization of employees’ voluntary efforts has become crucial to management ( Podsakoff, MacKenzie, Paine, & Bachrach, 2000). For this reason, management scholars have increasingly paid attention to organizational citizenship behaviour (OCB), which refers to various forms of extra-role, discretionary behaviour that may enhance organizational performance (Organ, Podsakoff, & MacKenzie, 2006). Although the potential contribution of OCB to unit or organizational performance has been the essential motivation of most OCB studies, thus far, the vast majority of them have been conducted at the individual level (Bommer, Dierdorff, & Rubin, 2007). In a departure *Correspondence should be addressed to Professor Yuhyung Shin, College of Business Administration, Hanyang University, 17 Haengdang-dong, Sungdong-Ku, Seoul, 133-791, Republic of Korea (e-mail: yuhyungshin@hotmail.com). The British Psychological Society 531 Journal of Occupational and Organizational Psychology (2010), 83, 531–552 q 2010 The British Psychological Society www.bpsjournals.co.uk DOI:10.1348/096317909X440233