What we refer to as diagnosis in this article is the attempt to gather data to compare a given team or organization against a prescriptive model or desired future state. Methodologies congruent with these assumptions, such as classical OD action research, sociotechnical systems analysis, survey feedback, task-oriented team development, and SWOT (strengths, weaknesses, opportunities, and threats) analysis are then employed to help guide problem solving, decision making, and action planning. The assumption that there are objective data that can be used in a process of social discovery, therefore, is a central aspect of the change process in Diagnostic OD. As we next discuss, these bedrock premises and practices are now being challenged by newer OD practices operating implicitly or explicitly from other assumptions.