We have reviewed theories and research in the area of contagion with an emphasis on definitions of contagion. The review shows that a great deal of the confusion surrounding the term is due to the fact that the phenomena involved in contagion are extremely heterogeneous, yet they typically have been placed under homogeneous rubrics. Accordingly, we propose herein that contagion should be conceptualized as a general type, social contagion, and three subtypes: disinhibitory, echo, and hysterical. In this article, we have distinguished social contagion and its subtypes from other types of social influence phenomena and reclassified theoretical and research articles under the newly proposed definitions. The proposed reconceptualization shows how contradictions in the literature can be resolved by distinguishing the type of contagion in question and provides the foundation for a more comprehensive and useful psychology of contagion.