By definition, the informal economy is hard to study, especially in developing countries. This excellent book uses state-of-the-art methodologies and recently available data to measure and analyze informality in advanced economies and emerging market and developing economies. In particular, it explores the business cycles in the informal sector in 160 countries over the past 30 years; the study is the first one to show that cycles in the formal economy cause those in the informal economy. Contrary to the widespread stereotype that the informal sector is a buffer that helps to mitigate recessions in the formal sector, the informal sector's output moves in sync with the formal one, and informal employment does not increase during recessions. This book also produces the first analysis of the role of informality during the COVID-19 pandemic. Informal economic activity is concentrated in labor-intensive service sectors and thus is especially vulnerable to social distancing and lockdowns. A rigorous, relevant, and highly timely must-read for development scholars and policy makers.