I am currently working on an introductory chapter to a collection I have prepared for my publisher (Edward Elgar) which describes the evolution of Modern Monetary Theory (MMT). The task might appear to be straightforward but in fact is rather vexed. There is considerable dispute as to where the roots lie. A specific debate is the importance of the work of John Maynard Keynes. Many Post Keynesians, almost by definition, believe that Keynes was a central figure in the development of what we now call Post Keynesian economics, although that ‘school of thought’ evades precise identification and is certainly anything but homogenous. There are MMT proponents, who while sympathetic with much of Post Keynesian theory, disagree on key propositions – specifically relating to debt and deficits (as an example). But then they also point to Keynes’ work as seminal in the development of MMT. My own view is that many of the important insights in Keynes were already sketched out in some detail in Marx. Further, the work of the Polish economist Michał Kalecki was much deeper in insight than the work of his contemporary, Keynes. But for me the real sticking point against Keynes was his view that fiscal deficits should be balanced over the business cycle and that would allow governments to pay back debt incurred in the deficit years. That view has crippled progressive thought ever since and is antithetical to MMT. The debate also has resonance with the current leadership struggle within the British Labour Party about fiscal deficits and the claims by the ‘socialist’ candidate, Jeremy Corbyn that he will “balance the budget” when unemployment is low so as to avoid inflation. This view derives from the adoption by progressives of Keynes’ views, whether they know that or not. It is a mistaken view and retards progressive policy development.