Process theory is a commonly used form of scientific research study in which events or occurrences are said to be the result of certain input states leading to a certain outcome (output) state, following a set process.

Process theory holds that if an outcome is to be duplicated, so too must the process which originally created it, and that there are certain constant necessary conditions for the outcome to be reached. When the phrase is used in connection with human motivation, process theory attempts to explain the mechanism by which human needs changes. Some of the theories that falls in this category are Expectancy theory, Equity theory, and Goal setting.