In this chapter, Spielberger, Krasner, and Solomon concentrate upon the sensation that is called anger, hostility, or aggression. They liken anger to a state emotion and hostility to a trait, whereas the label aggression is reserved for the behavioral expression of the first two. They refer to the structure of these three concepts as the AHA! Syndrome. The chapter begins with a thorough review of the history of the relationship between anger and psychosomatics. Also featured is a discussion of the role of anger in the Type A behavior pattern and on the nature of anger itself. Following a brief review of the history of attempts to measure hostility and anger, we are introduced to the State-Trait Anger Scale (STAS) developed by Spielberger and his colleagues. The authors then provide an in-depth review ofresearch and thinking on the nature of the expression of anger; that is, whether it is directed inward (suppressed) or outward (expressed). The nature and meaning of the control of anger is also reviewed. We are presented with the principal psychometric data related to the development of the Anger EXpression Scale (AX), which measures anger-in, anger-out, and angercontrol. In concluding, the authors explain the need for scales such as the ST AS and AX and describe their usefulness in individual difference and health research.-EDITOR Anger, hostility, and aggression have long been regarded as important factors in essential hypertension and coronary heart disease (see Diamond, 1982). Almost 50 years ago, Franz Alexander (1939) theorized that the strenuous efforts of hypertensives to suppress their angry feelings resulted in chronic activation of the cardiovascular system, and, eventually, to fixed elevations in blood pressure. Impressive evidence of a strong relationship between suppressed hostility ("anger-in") and hypertension has also been reported by Harburg and his associates (Esler et al., 1977; Gentry, Chesney, M. P. Janisse (ed.), Individual Differences, Stress, and Health Psychology