In the last few years, Web sites have evolved from a simple collection of hypertext pages towards applications supporting complex business processes. Although it is still easy to publish a couple of pages, more and more it is recognized that appropriate design methods are needed to develop more complex Web sites. In the past, Web sites were created opportunistically without prior planning or analysis, and without any regard for methodology, resulting in the classical maintenance problems and development backlog. At the same time, a new problem unknown in classical information systems emerged: competition for the visitor’s attention. Especially for commercial Web sites, it is important to hold the interest of the visitors and to keep them coming back. As stated by usability expert Jakob Nielsen: “all the competitors in the world are but a mouse click away” (Nielsen, 2000). Much more than in “classical” software systems, the usability of Web sites is a primary factor for their success.