Different models of change reflect different assumptions about information systems development, implementation, and research. These models inform the work of system development and implementation (Kaplan 1991). In one of these groups of models, Research, Development, and Diffusion (RDD) models, experts develop a system they consider beneficial, and users either adopt it or are considered resistant to it. In Problem Solving (PS) models, which derive from Lewin’ theories of group dynamics and change, experts and clients work together to develop information systems solutions to what they perceive as problems. In Social Interaction (SI) models, which are based on Rogers’s Classic Diffusion Theory, the emphasis is on how an innovation is communicated through social channels over time. New design methodologies and new evaluation approaches replace RDD models with PS or SI models. These models address social, cultural, political, or work life issues in system design and in system evaluation. methodologies and approaches.