Fuel cell systems are a new promising type of on-site power generation technology that offers modularity, efficient operation across a wide range of conditions, minimal environmental impact, and opportunities for integration into combined heat and power (CHP) and combined cooling, heat and power (CCHP) systems. These systems offer a number of advantages, which include economic benefits, better utilization of energy resources, and reduced environmental impact. The application of CHP and CCHP systems in buildings requires the selection of an operating strategy, coordination with local utility systems, and evaluation of the economic value of the system. By understanding fuel cells and CHP and CCHP systems, building engineers can identify appropriate applications that will yield economic and environmental benefits for their clients and for society.