Usability is integral to software quality. Software developers increasingly acknowledge the importance of user-centered, Web site development. The value of usability engineering and the role of the usability engineer (UE) are less understood. A common assumption is that the UE’s role is only to be a user advocate. To this role, we add the responsibility of addressing concerns of other stakeholders in Web site design and development. We discuss usability engineering and the processes that it encompasses, such as project planning, requirements definition, user-centered design (UCD) and evaluation/testing within the context of traditional software engineering lifecycles. We define the UE’s role throughout a user-centered, Web site development lifecycle. This lifecycle integrates compatible usability engineering processes into software engineering processes, drawing examples from research and experience.