The aim of this paper is to present the architecture, the algorithms and the performance results of an integrated indoor environment energy management system (IEEMS) for buildings. The buildings' users comfort requirements are fulfilled and regulated using a fuzzy controller. The fuzzy controller's structure is adjusted to the users' requirements that are monitored via a smart card system. The IEEMS is installed in two buildings in Athens and in Crete, both in Greece. The energy conservation achieved by the IEEMS operation is more than 30% compared to the existing control system. (C) 2004 Elsevier B.V. All rights reserved.