E-commerce is an ever-growing way of making trade. By its very nature, it dif-fers from traditional bricks-and-mortar stores, in both good and bad. Tremen-dous international competition in e-commerce forces online retailers to think carefully how to affect the customer´s purchase intentions. In this Bachelor´s Thesis, usability´s effect on e-commerce was investigated. The study was con-ducted as a literature review, which is based on literature found on e-commerce and usability. E-commerce is a fairly new phenomenon, so the litera-ture which concerns it does not need to be screened out. This thesis focuses on-ly on business-to-customer e-commerce because otherwise the addressed view would be too broad. When examining the effect of usability on e-commerce´s success, four issues emerged, each of which contributes to the customers buy-ing intentions. These included the utilitity, ease-of-use, reliability and risks which customer feels about the web shop, which is used. Usability planning can contribute to all these aspects. It turned out that good usability also influ-ences the loyality, which customers give out to websites. This thesis is aimed especially at online retailers and stakeholders of online retailers, for an exam-ple customers and investors.