This book seeks to offer the general reader a clear and concise introduction to the Matthew effect, one of the least known but most important principles in the social sciences. Matthew effects are said to occur when social advantages lead to further advantages— or disadvantages to further disadvantages—through time, creating widening gaps between those who have more and those who have less. It has been more than forty years since the eminent sociologist Robert K. Merton of Columbia University coined the term to describe circumstances in which the rich get richer and the poor get poorer, as the saying goes. Matthew effects are not confined to the economic sphere, however; they have been observed across a broad spectrum of social institutions. Thus the principle is essential to understanding the social dynamics of inequality in general.