The usefulness of the social class construct for life-cycle research is discussed in this paper. Social class is defined as used in the paper, and as it is generally used by students of the human life cycle. It is further evaluated as a descriptor, and a predictor of behaviors and attitudes. The construct seems to be most useful in studies of adults rather than children, and though it possesses important limitations as a predictor, it is the most pervasive of the group variables in its influence on behavior and attitudes. Social class and its relation to social structure, social distance, social mobility, social change, poverty, and conflict are also included. (Author/DM)