Book excerpt: Over the course of the last four decades, Robert Cialdini's work has helped spark an intellectual revolution in which social psychological ideas have become increasingly influential. The concepts presented in his book, Influence: The Psychology of Persuasion, have spread well beyond the geographic boundaries of North America and beyond the field of academic social psychology into the areas of business, health, and politics. In this book, leading authors, who represent many different countries and disciplines, explore new developments and the widespread impact of Cialdini's work in research areas ranging from persuasion strategy and social engineering to help-seeking and decision-making. Among the many topics covered, the authors discuss how people underestimate the influence of others, how a former computer hacker used social engineering to gain access to highly confidential computer codes, and how biology and evolution figure into the principles of influence. The authors break new ground in the study of influence.