This article gives an introduction to the field of impact research. After a short discussion of the role of information in organizational context, the interaction perspective on impact research is presented. Empirical research results in the field of impacts of IT on internal organization in 11 organizations in the fields of banking, services, government and industry are presented. In general the systems studied were useful in realizing more centralization and impersonal control. Professionals seemed to be very pleased with information systems, because they avoided tedious jobs and organizational bottle-necks, and gave them opportunities to do their work in a better way. This is very different from the experiences of non-professional workers, who met with more routinization, rigidity and job dissatisfactions. Competitiveness was very often increased due to big cost savings and better service to clients. The authors note that much extra research is needed, especially for making more accurate estimates of impacts and how they occur. This should become an integral part of systems development and information management practice in the future.