Concern about inequality, particularly inequality of income and wealth, has become prominent in public discourse around the world. This article first discusses issues of measurement and goes on to ask why we should care, emphasizing fairness and the market distortions and negative externalities found in unequal societies. It documents that the decline in global inequality in recent decades has been due to falling inequality between, rather than within, countries. The popular picture of rising inequality in OECD countries is more varied and complex than often perceived. Its drivers include aspects of globalization and of technological change as well as changes in the distribution of market power, in financial markets, public policy, and monetary policy. There are two over-arching questions about how governments can address inequality. The first is what should be tackled at the international level and what should be the preserve of national policy. The second is what should be the balance between pre- and post-market interventions. Both have a role but generally the balance has been too skewed towards the latter.