Much of the recent work and progress in CFTs has been at zero temperature and it is highly desirable to extend this to finite temperature/finite size systems. This is not only dictated by the obvious relevance of finite temperature systems to the real world, but also by important theoretical questions. This includes fundamental issues regarding the thermalisation process of quantum systems, the holographic description of black holes in terms of finite temperature CFTs, and the intriguing relationship between thermal CFT partition functions and modular functions. Although disparate at first sight, these areas are converging to a common theme involving the study of thermal CFT correlation functions.