Type A and Type B personality hypothesis describes two contrasting personality types. In this hypothesis, personalities that are more competitive, highly organized, ambitious, impatient, highly aware of time management, or aggressive are labeled Type A, while more relaxed, "receptive", less "neurotic" and "frantic" personalities are labeled Type B.

The two cardiologists, Meyer Friedman and Ray Rosenman, who developed this theory came to believe that Type A personalities had a greater chance of developing coronary heart disease. Following the results of further studies and considerable controversy about the role of the tobacco industry funding of early research in this area, some reject, either partially or completely, the link between Type A personality and coronary disease. Nevertheless, this research had a significant effect on the development of the health psychology field, in which psychologists look at how an individual's mental state affects physical health.