Abstract-Knowledge sharing research has proposed various theories and explanations regarding individuals' intentions to share knowledge in virtual distributed communities. Although past research studies can provide useful insights into the factors that significantly affect knowledge sharing intention, there are some discrepancies of findings among the different studies. The main purpose of this paper is to review the previous empirical research studies to first identify the main theories and factors used to explain online knowledge sharing. The findings suggest that these incentive items could be grouped into three main categories: personal factors (knowledge self-efficacy, perceived relative advantage, perceived compatibility), social factors (trust, reciprocity, social network ties), and organizational factors (formal incentive mechanism). Of these factors, trust has been the most widely discussed, followed by social network ties. Next, this paper presents several main discrepancies among past research studies in order such as the notion of perceived compatibility, norm of reciprocity, and trust to provide possible directions for future studies.