The middle class refers to a class of people in the middle of a social hierarchy, often defined by occupation, income, education, or social status. The term has historically been associated with modernity, capitalism and political debate. Common definitions for the middle class range from the middle fifth of individuals on a nation's income ladder, to everyone but the poorest and wealthiest 20%. Theories like "Paradox of Interest" use decile groups and wealth distribution data to determine the size and wealth share of the middle class.

From a Marxist standpoint, middle class initially referred to the 'bourgeoisie,' as distinct from nobility. With the development of capitalist societies and further inclusion of the bourgeoisie into the ruling class, middle class has been more closely identified by Marxist scholars with the term 'petite bourgeoisie.'

There has been significant global middle-class growth over time. In February 2009, The Economist asserted that over half of the world's population belonged to the middle class, as a result of rapid growth in emerging countries. It characterized the middle class as having a reasonable amount of discretionary income and defined it as beginning at the point where people have roughly a third of their income left for discretionary spending after paying for basic food and shelter.