Keynes's thought on public intervention in the economic system has been rediscovered during the economic crisis that is devastating the world economy. Many opinion makers have appealed to go back to Keynesian monetary and fiscal policy. But who was John Maynard Keynes, and what is his legacy? Moreover up to which extent this latter may be useful in dealing with economic crisis in an era when, paraphrasing Keynes, «the development of a country becomes the by-product of the activities of a casino»?