The sociology of knowledge is the study of the relationship between human thought, the social context within which it arises, and the effects that prevailing ideas have on societies. It is not a specialized area of sociology. Instead, it deals with broad fundamental questions about the extent and limits of social influences on individuals' lives and the social-cultural basis of our knowledge about the world. The sociology of knowledge has a subclass and a complement. Its subclass is sociology of scientific knowledge. Its complement is the sociology of ignorance.

Knowledge is an awareness of facts, a familiarity with individuals and situations, or a practical skill. Knowledge of facts, also called propositional knowledge, is often characterized as true belief that is distinct from opinion or guesswork by virtue of justification. While there is wide agreement among philosophers that propositional knowledge is a form of true belief, many controversies focus on justification. This includes questions like how to understand justification, whether it is needed at all, and whether something else besides it is needed. These controversies intensified in the latter half of the 20th century due to a series of thought experiments called Gettier cases that provoked alternative definitions.