Effective investigations of user requirements for products and services are most often discussed in terms of which method to use. Nevertheless, when user investigations are planned and carried out in a system design context, several related aspects must be considered. For example: Which users should be included? Where should the study be carried out? How should data be collected? and What kind of information is relevant to what stage of the design process? In this paper, the concept of triangulation is introduced as a 'conceptual tool' for managing the multidimensionality of user requirements investigations. To illustrate how triangulation works, a case study of the user requirements investigation process for a home-shopping service system is presented. Three types of triangulations: location, knowledge, and methodological triangulation are identified and defined, and are proven appropriate in the characterization of strategies of user requirements investigations. Moreover, the concept of triangulation as a means for increasing the reliability of a user requirement investigation, as well as some underlying factors in determining a triangulation strategy are discussed.