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. 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 and perceived compatibility), social factors (trust, reciprocity and social network ties) and organizational factors (formal incentive mechanism).