Most formulations of strain are unsystematic. We do not possess, for instance, an exact classification of types of strain. Nor do we know the relations among the major types of strain. Perhaps most important, we have no adequate theory of how strain combines with other determinants-conduciveness, growth of beliefs, operation of social controls, for instance-in the rise of an episode of collective behavior. In this volume we hope to lessen these deficiencies. In this chapter we shall define strain as an impairment of the relations among and consequently inadequate functioning of the components of action. To give technical meaning to this definition we shall develop and illustrate a classification of types of strain on the basis of the categories developed in the last chapter. In later chapters we shall discuss the complex interaction among strain and the remaining determinants.