This paper reports the outcomes of a three year study into the requirements process, an important but poorly understood part of systems development. Humans play an essential role in determining requirements yet few models of the requirements process include human actors. This paper presents an understanding of the requirements process expressed in a descriptive model that integrates the social and technical aspects of the requirements process. The model comprises five key areas: the problem domain, analysts’ domain, requirements sub-processes, problem space and management of the requirements process. The model may be used to support, manage and improve the requirements process in practice.