Four billion low-income consumers, a majority of the world s population, constitute the base of the economic pyramid (BOP). New empirical measures of their aggregate purchasing power and behavior as consumers suggest significant opportunities for market-based approaches to better meet their needs, increase their productivity and incomes, and empower their entry into the formal economy. This volume, based on unique access to the household income and consumption surveys of developing and transition countries, offers a new and compelling perspective on low-income communities worldwide. Drawing on income data from 110 countries and standardized expenditure data from 36 countries across the globe, The Next 4 Billion is an important first look at the market opportunity represented by four billion individuals who make up the BOP. The analysis for the first time provides a quantitative assessment and characterization of BOP markets, at several levels of analysis.