This paper describes the requirements handling process of a set of research projects, the ATHENA IP, and how this process is supported by modeling and visualizing requirement structures. First, users and external stakeholders register requirements through easy-to-use Web interfaces. Then developers and managers utilize an integrated modeling tool for visual classification, analysis, elicitation, and selection of requirements. In this paper, we show how advanced visualization techniques improve and support state-of-the-art within requirements handling. This requirement handling system was first applied in the UEML project, and a variant of it is in day-today use by a commercial software vendor and its customers. We finally describe the overall experiences from use of the system.