First published in 1955, Personal Influence reports the results of a pioneering study conducted in Decatur, Illinois, validating Paul Lazarsfeld’s serendipitous discovery that messages from the media may be further mediated by informal opinion leaders who intercept, interpret, and diffuse what they see and hear to the personal networks in which they are embedded. This classic volume set the stage for all subsequent studies of the interaction of mass media and interpersonal influence in the making of everyday decisions in public affairs, fashion, movie-going, and consumer behavior. The contextualizing essay in Part One dwells on the surprising relevance of primary groups to the flow of mass communication. Peter Simonson of the University of Pittsburgh has written that Personal Influence was perhaps the most influential book in mass communication research of the postwar era, and it remains a signal text with historic significance and ongoing reverberations…more than any other single work, it solidified what came to be known as the dominant paradigm in the field, which later researchers were compelled either to cast off or build upon. In his introduction to this fiftieth-anniversary edition, Elihu Katz discusses the theory and methodology that underlie the Decatur study and evaluates the legacy of his coauthor and mentor, Paul F. Lazarsfeld.