Online trust is a critical element to the success of electronic commerce (e-commerce). Indeed it reduces the level of uncertainty that arises because of the lack of face-to-face interactions with vendors. In ecommerce purchaser-vendor interactions are subject to uncertainty, anonymity, and communication means reliability. This chapter discusses how some trust models have been developed to address these issues. Some models promote familiarity and competitiveness as part of the exercise of assessing online trust. This assessment uses fuzzy logic-based techniques. © 2009, IGI Global.