The notion that the demand and supply side are independent is a key feature of textbook undergraduate economics and of modern macroeconomic models. Economic output is thought to be constrained by the productive capabilities of the economy - the ‘supply-side' - through technology, demographics and capital investment. In the short run a boost in demand may increase GDP and employment due to frictions such as sticky wages, but over the long-term successive rises in demand without corresponding improvements on the supply side can only create inflation as the economy reaches capacity. In this post I will explore the alternative idea of demand-led growth, where an increase in demand can translate into long-run supply side gains. This theory is most commonly associated with post-Keynesian economics, though it has been increasingly recognised in the mainstream literature.