Electronic commerce (e-Commerce) has exploded on the Internet over the past few years and is expected to continue growing at an exponential rate (Kannan, Chang and Whinston, 1998; Fellenstein and Wood, 2000). According to the GVU’s 8th WWW User Surveys (1997), the most important issues facing online users are privacy (31%), censorship (24%) and navigation (17%). Since user interface design directly impacts navigation and affects the user’s interaction with a Web site, this chapter will explore a number of different factors that affect user interface design on the World Wide Web. In all there are six factors that we explore in this chapter. They are the user’s mental model as newly defined and focused upon perception and conception (Haynes and Mahfouz, 2001), the level of expertise of the user, the user’s learning style, the richness of the media used, the organizational image and message, and the user’s intentions. All these factors involve internal (to the Web page design) and external (to the user’s environment) implications that impact user interface design on the Internet. Since all factors are external with the exception of the richness of the media used and, to some extent, the organizational image and message, it follows that we have chosen to emphasize in this chapter the external factors, namely those factors that directly relate to the user.