Energy storage in the walls, ceiling and floor of buildings may be enhanced by encapsulating suitable phase change materials (PCMs) within these surfaces to capture solar energy directly and increase human comfort by decreasing the frequency of internal air temperature swings and maintaining the temperature closer to the desired temperature for a longer period of time. This paper summarizes the investigation and analysis of thermal energy storage systems incorporating PCMs. for use in building applications. Researches on thermal. storage in which the PCM is encapsulated in concrete, gypsum wallboard, ceiling and floor have been ongoing for some time and are discussed. The problems associated with the application of PCMs with regard to the selection of materials and the methods used to contain them are also discussed. (C) 2003 Elsevier Ltd. All rights reserved.