A mental model is an internal representation of external reality: that is, a way of representing reality within the mind. Such models are hypothesized to play a major role in cognition, reasoning and decision-making. The term for this concept was coined in 1943 by Kenneth Craik, who suggested that the mind constructs "small-scale models" of reality that it uses to anticipate events. Mental models can help shape behaviour, including approaches to solving problems and performing tasks.

In psychology, the term mental models is sometimes used to refer to mental representations or mental simulation generally. The concepts of schema and conceptual models are cognitively adjacent. Elsewhere, it is used to refer to the mental model theory of reasoning developed by Philip Johnson-Laird and Ruth M. J. Byrne.

The term mental model is believed to have originated with Kenneth Craik in his 1943 book The Nature of Explanation. Georges-Henri Luquet in Le dessin enfantin (Children's drawings), published in 1927 by Alcan, Paris, argued that children construct internal models, a view that influenced, among others, child psychologist Jean Piaget.

Jay Wright Forrester defined general mental models thus:

The image of the world around us, which we carry in our head, is just a model. Nobody in his head imagines all the world, government or country. He has only selected concepts, and relationships between them, and uses those to represent the real system (Forrester, 1971).

Philip Johnson-Laird published Mental Models: Towards a Cognitive Science of Language, Inference and Consciousness in 1983. In the same year, Dedre Gentner and Albert Stevens edited a collection of chapters in a book also titled Mental Models. The first line of their book explains the idea further: "One function of this chapter is to belabor the obvious; people's views of the world, of themselves, of their own capabilities, and of the tasks that they are asked to perform, or topics they are asked to learn, depend heavily on the conceptualizations that they bring to the task."

Since then, there has been much discussion and use of the idea in human-computer interaction and usability by researchers including Donald Norman and Steve Krug (in his book Don't Make Me Think). Walter Kintsch and Teun A. van Dijk, using the term situation model (in their book Strategies of Discourse Comprehension, 1983), showed the relevance of mental models for the production and comprehension of discourse.

Charlie Munger popularized the use of multi-disciplinary mental models for making business and investment decisions.