The strategic HRM literature suggests that HRM infl uences employees in combinations of practices that "fi t" each other rather than as stand-alone practices; however, it pays little attention to the underlying individual-level mechanisms. In contrast, the HRM literature on knowledge sharing examines the infl uence of single practices on individual-level knowledge sharing, but fails to include the infl uence of combinations of practices. We link the idea of fi t between practices to employee motivation for knowledge sharing by arguing that rewards may be ambiguous and diffi cult to interpret, but that such ambiguity may be reduced if rewards are combined with other aligned HRM practices, notably job design and work climate. Thus, fi t is established through the ambiguity-reducing effect of combining specifi c HRM practices. Accordingly, we test for complementarities among rewards, job design, and work climate in the form of a three-way interaction among these variables with respect to their impact on knowledge-sharing motivation. Our analysis of 1,523 employees in fi ve knowledge-intensive fi rms shows that employees who are exposed to knowledge-sharing rewards experience higher levels of autonomous motivation to share when they are simultaneously exposed to a noncontrolling job design and work climate that support knowledge sharing.