This chapter gives an overview of the available cogeneration technologies and their performance. The basis of cogeneration is always that the bulk of the heat released during a process of converting fuel energy into mechanical or electrical energy is not wasted but economically used. The machine that converts the fuel into mechanical energy and heat is often called the prime mover. Common prime movers are gas turbines, reciprocating engines and more recently also fuel cells. Mechanical energy can be converted into electrical energy with an electric generator, whereas heat can be transformed into chill with an absorption chiller. Heat exchangers are an integral part of cogeneration installations. Heat pumps are also increasingly used in such installations.