An overview and historical evolution of both classical and state-of-the-art energy conversion technology. Advanced analysis of energy conversion hardware, air conditioning and refrigeration as well as fossil fuel combustion processes using concepts of exergy. Major methods of direct energy conversion are covered, including thermoelectricity, photovoltaics, thermionics, magnetohydrodynamics, and fuel cells. The current state of national and world energy is presented and alternatives including renewable energy and a hydrogen economy are explored with reference to economical, political, environmental and technological factors.