The theory of planned behavior (TPB) is a psychological theory that links beliefs to behavior. The theory maintains that three core components, namely, attitude, subjective norms, and perceived behavioral control, together shape an individual's behavioral intentions. In turn, a tenet of TPB is that behavioral intention is the most proximal determinant of human social behavior.

The theory was elaborated by Icek Ajzen for the purpose of improving the predictive power of the theory of reasoned action (TRA). Ajzen's idea was to include perceived behavioral control in TPB. Perceived behavior control was not a component of TRA. TPB has been applied to studies of the relations among beliefs, attitudes, behavioral intentions, and behaviors in various human domains. These domains include, but are not limited to, advertising, public relations, advertising campaigns, healthcare, sport management consumer/household finance, and sustainability.

Icek Ajzen (1985) proposed TPB in his chapter "From intentions to actions: A theory of planned behavior." TPB developed out of TRA, a theory first proposed in 1980 by Martin Fishbein and Ajzen. TRA was in turn grounded in various theories bearing on attitude and attitude change, including learning theories, expectancy-value theories, attribution theory, and consistency theories (e.g., Heider's balance theory, Osgood and Tannenbaum's congruity theory, and Festinger's dissonance theory). According to TRA, if an individual evaluates a suggested behavior as positive (attitude), and if he or she believes significant others want the person to perform the behavior (subjective norm), the intention (motivation) to perform the behavior will be greater and the individual will be more likely to perform the behavior. Attitudes and subjective norms are highly correlated with behavioral intention; behavioral intention is correlated with actual behavior.

Research, however, shows that behavioral intention does not always lead to actual behavior. Because behavioral intention cannot be the exclusive determinant of behavior where an individual's control over the behavior is incomplete, Ajzen introduced TPB by adding to TRA the component "perceived behavioral control". In this way he extended TRA to better predict actual behavior.

Perceived behavioral control refers to the degree to which a person believes that he or she can perform a given behavior. Perceived behavioral control involves the perception of the individual's own ability to perform the behavior. In other words, perceived behavioral control is behavior- or goal-specific. That perception varies by environmental circumstances and the behavior involved. The theory of planned behavior suggests that people are much more likely to intend to enact certain behaviors when they feel that they can enact them successfully.

The theory has thus improved upon TRA.

Along with attitudes and subjective norms (which make up TRA), TPB adds the concept of perceived behavioral control, which grew out of self-efficacy theory (SET). Bandura proposed self-efficacy construct in 1977, in connection to social cognitive theory. Self-efficacy refers to a person's expectation or confidence that he or she can master a behavior or accomplish a goal; an individual has different levels of self-efficacy depending on the behavior or intent. Bandura distinguished two distinct types of goal-related expectations: self-efficacy and outcome expectancy. He defined self-efficacy as the conviction that one can successfully execute the behavior required to produce the outcome in question. Outcome expectancy refers to a person's estimation that a given behavior will lead to certain outcomes. Bandura advanced the view that self-efficacy is the most important precondition for behavioral change, since it is key to the initiation of coping behavior.

Previous investigations have shown that a person's behavior is strongly influenced by the individual's confidence in his or her ability to perform that behavior. As self-efficacy contributes to explanations of various relationships among beliefs, attitudes, intentions, and behavior, TPB has been widely applied in health-related fields such as helping preadolescents to engage in more physical activity, thereby improving their mental health, and getting adults to exercise more.