Companies increasingly outsource activities to volunteers that they approach via an open call on the internet. The phenomenon is called ‘crowdsourcing’. For an effective use of crowdsourcing it is important to understand what motivated these online volunteers and what is the influence of rewards. Therefore, this thesis examines the effects of motivation and rewards on the participation and performance of online community members. We studied motivation, rewards and contributions in three crowdsourcing initiatives that varied in reward systems.

The findings of these three studies resulted in a refined model of the effects of rewards and motivation on voluntary behavior. With this model we provide a possible solution for contrary findings in empirical studies of online communities and the ongoing debate between two schools of cognitive psychology. Our results also have important implications for organizers of online communities, amongst others, regarding the effective application of reward systems. We also provide a crowdsourcing typology in which crowdsourcing initiatives are classified on the basis of their reward systems and identify the motivation profiles of optimal performers per crowdsourcing type