This dictionary entry defines the development of new Keynesian macroeconomics (NKM) since the 1980s. I argue that the key defining feature NKM is the introduction of imperfect competition, making price and/or wage setting endogenous and hence allowing for a rigorous understanding of nominal rigidity. This has led to a shift away from perfect competition in macroeconomics. The combination of NKM with dynamic macroeconomic modelling has led to the current orthodoxy: the new-neoclassical synthesis. Dynamic wage and price models lead to monetary neutrality in steady-state, non-neutrality out of steady-state. Other themes in NKM include efficiency wage theory and coordination failure.