Book excerpt: User Engagement (UE) is a complex concept to investigate. The purpose of this book is not to constrain UE to one perspective, but to offer a well-rounded appreciation for UE across various domains and disciplines. The text begins with two foundational chapters that describe theoretical and methodological approaches to user engagement; the remaining contributions examine UE from different disciplinary perspectives and across a range of computer-mediated environments, including social and communications media, online search, eLearning, games, and eHealth. The book concludes by bringing together the cross-disciplinary perspectives presented in each chapter and proposing an agenda for future research in this area. The book will appeal to established and emerging academic and industry researchers looking to pursue research and its challenges. This includes scholars at all levels with an interest in user engagement with digital media, from students to experienced researchers, and professionals in the fields of computer science, web technology, information science, museum studies, learning and health sciences, human-computer interaction, information architecture and design, and creative arts.