Expectancy theory (or expectancy theory of motivation) proposes that an individual will behave or act in a certain way because they are motivated to select a specific behavior over others due to what they expect the result of that selected behavior will be. In essence, the motivation of the behavior selection is determined by the desirability of the outcome. However, at the core of the theory is the cognitive process of how an individual processes the different motivational elements. This is done before making the ultimate choice. The outcome is not the sole determining factor in making the decision of how to behave.

Expectancy theory is about the mental processes regarding choice, or choosing. It explains the processes that an individual undergoes to make choices. In the study of organizational behavior, expectancy theory is a motivation theory first proposed by Victor Vroom of the Yale School of Management.

This theory emphasizes the need for organizations to relate rewards directly to performance and to ensure that the rewards provided are deserved and wanted by the recipients.

Victor H. Vroom (1964) defines motivation as a process governing choices among alternative forms of voluntary activities, a process controlled by the individual. The individual makes choices based on estimates of how well the expected results of a given behavior are going to match up with or eventually lead to the desired results. Motivation is a product of the individual's expectancy that a certain effort will lead to the intended performance, the instrumentality of this performance to achieving a certain result, and the desirability of this result for the individual, known as valence.