A stylized prediction of the development economics discourse is that informality will disappear with development, and yet in the last 20 years conventional measures of informality, far from declining, have either remained stagnant or have actually increased. This includes countries such as India where economic growth has been at historically high levels. What exactly is informality and what are its magnitudes and trends? What are the causes of informality and why is it not decreasing as predicted by standard theories of development? What are the consequences for inclusive economic growth of a large and increasing informal sector? What are feasible and desirable policy responses to informality? These are the questions that motivate this broad based overview of informality. The questions will be addressed based on recent and ongoing research on India and globally.