After an introduction which summarises the key global energy issues, a brief overview is provided with respect to the past 3 main periods which have characterised the development of nuclear energy from the first commercial plant in 1954 up to the present days. The worldwide situation at end of January 2011 is  given with respect to the reactors in operation and under construction. With reference to the plants in operation, the programs underway for the life extension from around 40 to 60 years it is reported with the relevant positive effects on cost of electricity production and contribution to the reduction of CO2 emissions. With respect to new plants, the reactors available on the market are presented together with the various components of the kWh cost (investment, O&M, fuel cycle and final waste disposal): the main development programs in the various countries are reported. The cost of kWh production from nuclear is compared to the one from other fossil fuel or renewable plants, considering a wide range of variation of fuel and CO2 emission costs. After some considerations on Uranium resources and on final waste disposal, some conclusions are drawn together with some considerations on the Italian nuclear approach/situation.