A human being spends approximately one-third of his/her life in sleep. Sleep can help people overcome tiredness, and is very important to one's memory. With the gradual understanding of the influence of thermal parameters in a sleeping environment on the quality of sleep, different thermal environmental control approaches, such as electric blankets, space heating for cold sleep environments and circulation fans and air-conditioning for hot sleep environments, have been used to maintain a suitable thermal environment for sleep, so that sleep quality could not be adversely affected. In this review paper, firstly, the concept of thermal comfort applicable to sleeping environments is introduced and the relevant studies reviewed. Secondly, the review of the two important issues related to air-conditioning for sleeping environments in tropics and sub-tropics, i.e., night-time space cooling load characteristics, and ventilation requirement for a sleeping person, is presented. Thirdly, different air-conditioning systems used in sleeping environments and these related energy consumptions are reviewed, with an emphasis on bed-based (task/ambient conditioning) TAC applicable to a sleeping environment, which could help save more energy without scarifying the thermal comfort of a sleeper and indoor air quality. Finally, a number of research areas where future studies are needed are reported, including developing optimized control strategies for air-conditioning systems for sleeping environments according to night-time space cooling load characteristics, and new TAC systems applicable to a sleeping environment for greater energy saving. (C) 2013 Elsevier Ltd. All rights reserved.