In this introductory chapter, we briefly introduce the reader to the mystery that continues to surround both laughter and humor, and then describe the path we shall take to finally resolve it. We summarize each of the subsequent 11 chapters: Ancient Wisdom and Modern Insights (evaluating prominent existing theories); Communication at Its Core (arguing why laughter must be viewed as conveying a message); The Heart of the Mutual Vulnerability Theory (the connection between laughter and perceived vulnerabilities, plus its “dual” nature); Humor and Its Relationship to Laughter (seeing humor as attempts to intentionally inspire feelings of amusement); Detecting Vulnerability (understanding variation in laugh responses based on whether one perceives vulnerability); Group Dynamics and Their Influence (variation due to the current social context); The Search for Laughter’s Origins (when and how laughter first arose as a behavior); The Evolution of Laughter and Humor (how their use and complexity has increased over time); Some Implications of the MVT (reconciling with older theories and understanding bullying behavior); The MVT as Guide (misinterpreting laughter, laughter skills, and what laughter says about us); and Going Forward (reviewing supporting evidence for the MVT, how it can be further tested, and some final thoughts).