Over the course of analyzing data from a series of socio-technic al ICT studies, we have developed a multi-dimensio nal concept of a social actor to guide qualitative data collection and analysis. Three information and communication technology (ICT) studies have been used to develop and refine the concept: a mid-1990's study of online information services use, a 4year study of intranet development and use, and a 5-year study of ICT use in collaborative networking among scientists in academia and industry. The social actor concept has been theoretically supported by institutionalist approaches. However, in our continuing effort to formalize it, we have found that alternative, and equally convincing, supporting theoretical explanations can be put forward using actor-network theory (ANT), as well as structuration theory. In this paper, we explain the social actor using ANT concepts and structuration theory concepts, and then contrast these with institutionalist concepts, emphasizing where ANT and structuration theory provide added value and suggest directions for further research and conceptual refinement.