The relationship between individual and collective behavior was perhaps first examined by Émile Durkheim, a scholar of social order and integration who theorized a “collective conscience” of beliefs and sentiments universal to a people in society. In the first essay of this volume, Alexandra Howson updates the continuing influence of Durkheim’s theories in the study of social arrangements and collective actions. Collective behavior exhibits, in universal or local contexts, conditions specific to the collective. In other words, individuals may act quite differently as a social organism. The following three essays introduce early theories on the formation of crowd dynamics, such as the contagion, convergence, and emergent norm theories. Richard Savage reviews contagion theory, which emerged in the late-nineteenth- century to explain how emotions and actions displayed by individuals in groups can become “contagious” and spread to other members. In the latter period of the twentieth century, this dynamic was employed to explain a variety of social phenomena from fashion fads to political protests. Convergence theory, as Jonathan Christiansen explains, reveals how certain character traits magnetize like-minded individuals to form groups. Lastly, emergent norm theory responds to the limits of the convergence theory and defines crowd behavior—rather than a violation of a dominant norm—as the construction of an emergent norm appropriate to the “changing and often chaotic situations of collective behavior episodes.” The research in “collective memory” represents the most recent interdisciplinary developments in the field. The most concrete examples are found in the creation of monuments and memorials, which serve as objects around which memories are solidified.