John Maynard Keynes is the 20th century's greatest economist. He sparked an intellectual revolution that transformed economic theory and policymaking. This book, written in plain English with minimal mathematics, is a concise and probing account of his major ideas. Keynes, argues Mark Hayes, showed that economics is a science of thinking in terms of models, in which progress depends on recognising when established models have become obsolete and new ones are required. Hayes outlines how Keynes did this, tracing his progression from the 'Classical' model that he inherited through to his masterpiece, The General Theory of Employment, Interest and Money, and beyond. The intellectual narrative is placed in its historical context, from the Versailles Peace Conference in 1919 to Bretton Woods. The final chapters consider the impact of Keynes's legacy, including his relevance to reform of the Euro. This accomplished study is not only a comprehensive introduction for students and general readers, but also a crystal-clear demonstration of how Keynes' thought is vital to understanding why contemporary economics needs to discard its old models and embrace profound change.