A thorough review of trust models is carried out in this paper to reveal the key capabilities of existing trust models and compare how they differ among disciplines. Trust decisions are risky due to uncertainties and the loss of control. On the other hand, not trusting might mean giving up some potential benefits. Advances in electronic transactions, mutliagent systems, and decision support systems create a necessity to develop trust and reputation models. The development of such models will allow for trust reasoning and decisions to be made in situations with high risk and uncertainty. In recent years, several attempts have been made to model reputation and trust. However, perceiving trust differently and the lack of having a unified trust definition are among the main causes of the proliferation of many trust models across different disciplines.