This paper reviews some leading novel energy conversion approaches which are aimed at improving power generation efficiency and/or reducing harmful emissions. Some of the concepts used for cycle improvement are higher top temperatures, improved combustion systems, evasion of the Carnot limit by integration with fuel cells and direct nuclear energy conversion to power (the nuclear generator), reduction of exergy destruction by staging and the use of exergy-efficient combustion processes, the use of lower temperature heat sinks and the use of renewable, environmentally-benign energy sources. Some of the systems described in this paper are hybrid multi-temperature source cycles (including the hybrid solar-powered/fuel-assisted Rankine cycle), high-temperature chemical gas turbine cycles, fuel-cell-topped Rankine cycles, high temperature ejector-topping power cycles and hybrid nuclear/fossil fuel power generation systems. The use of space (the extra-terrestrial environment) for energy conversion improvement is also discussed.