Chapter 1 reviews previous research on theory groups and argues that the social network methods that have been the dominant means of investigating them cannot adequately capture the significance of small-group interactions or the emergent generation of novel ideas from within theory groups. Understanding theory groups instead requires conceptualizing them from a microsociological, localistic perspective that considers the importance of group dynamics, group cultures, collective emotions, collective identity, and collective ideation. This allows for drawing direct connections between specific social interactions and the social construction and transformation of scientific theories, fields, and movements. I reconceptualize theory groups as small groups, as engines of collective action, and as faith-based collectives. The chapter closes by relating my analytic approach, research questions, and outlining the plan of the book.