This book contributes to our understanding of a number of theories and models. The theoretical contribution of this book is that it analyzes and synthesizes the relevant literature in order to enhance knowledge of IS theories and models from various perspectives. To cater to the information needs of a diverse spectrum of readers, this book is structured into two volumes, with each volume further broken down into two sections.The first section of volume 1 presents detailed descriptions of a set of theories centered around the IS lifecycle, including the success model, technology acceptance model, user resistance theories, and four others. The second section of volume 1 contains strategic and economic theories, including a resource-based view, theory of slack resources, portfolio theory, discrepancy theory models, and eleven others.