This chapter focuses on living laboratories, which are self-designated spaces capable of hosting real world experiments in built design and sustainable technologies. But living labs for low carbon research are emerging all over the world. It also explores the practices through which living laboratories are established and how those involved perceive their role, in order to better grasp how they might contribute to the retrofit agenda and the wider low carbon transition of which it forms part. It has outlined how and why claims are constructed by a range of actors, and explored the implications that experimentation in the real world holds for a wider low carbon transition. The chapter also presents an analysis of six living labs namely Queens Building, Salford Energy House, Arcosanti, North Desert Village, Elmer Avenue, Oxford Road Corridor in the UK and USA that focus on retrofitting urban environments.