The main objective of this study was to test the effects of two types of beliefs about knowledge sharing, i.e., individual and collective, on the intention and behavior of knowledge sharing. In addition, this study considered the moderating roles of organizational support and training among variables. Data were obtained from 1056 participants (55.7% women and 44.3% men), all of whom were knowledge workers. A model was constructed for the relationships between the variables. The results showed that collective beliefs about knowledge sharing were good predictors of knowledge sharing intention and behavior. By contrast, individual beliefs about knowledge sharing were not good predictors of knowledge sharing intention and behavior. The results also indicated moderating roles for training and organizational support. Finally, the knowledge sharing intention predicted knowledge sharing behavior. The results of this study improve our understanding of the human factors involved with knowledge sharing.