The book introduces a new approach to macroeconomics based on endogenous market structures (EMSs), with a close focus on business cycles, international trade and policy and growth. Chapter 1 reviews the standard neoclassical approach to macroeconomics. Chapter 2 extends it to EMSs with strategic interactions and endogenous entry of firms. Chapter 3 introduces EMSs in a model of the business cycle, shows that they allow us to outperform RBC models in explaining the cyclical variability of US data, and studies fiscal and monetary policy. Chapter 4 introduces EMSs in international trade, applies them to a dynamic framework and derives implications for trade policy, R&D policy and exchange rate policy. Chapter 5 introduces EMSs in the competition for the market and in the theory of Schumpeterian growth and provides an empirical test of the EMSs approach. Chapter 6 concludes with a non-technical discussion of the main results and employs them to discuss a number of recently debated issues.