Theory groups are small research groups who develop a new scientific theory and work together to promote its acceptance by the scientific community. This book offers a pioneering analysis of theory groups by reconceptualizing them as socio-emotional collectives characterized by evocative group cultures and emergent small group processes that enable their members to conceptualize new theories and champion new intellectual movements that cut against the status quo in their fields. Utilising data from a fifteen-year, multi-sited ethnography of a theory group in sustainability science, it investigates the significance of faith, solidarity, fun, and flow episodes for developing transformative science. Chapters also explore the importance inter-generational group dynamics for advancing new theories, and of specific geographic locations such as remote islands for fostering creativity. This gripping first-hand account is an essential read for those wishing to understand the conditions that support transformative scientific creativity and the social dynamics of intellectual movements.