Reformism is the belief that gradual changes through and within existing institutions can ultimately change a society’s fundamental economic system and political structures. This hypothesis of social change grew out of opposition to revolutionary socialism, which contends that some form of revolution is necessary for fundamental structural changes to occur.

Reformism is to be distinguished from pragmatic reforms: reformism is the assumption that an accumulation of reforms can lead to the emergence of an entirely different socioeconomic system than the present-day forms of capitalism and democracy, whereas pragmatic reforms represent attempts to safeguard the status quo against fundamental and structural changes.