Nuclear power provides nearly 6 per cent of the world’s primary energy at present. This chapter looks at the basics of nuclear power and at how it developed up to the turn of the century. The message at that point seemed to be that it was likely to decline as a major energy source due to the economic and safety problems that had emerged. We look at them in some detail. The next chapter then asks, given that its use does not generate carbon dioxide, can nuclear power can be relied on to play an increasing role in combating global warming, or whether, as many environmentalists would prefer, it should be phased out?