This book draws from a foundation of positive psychology and recently emerging positive organizational behavior (POB). Its purpose is to introduce the untapped human resource capacity of psychological capital, or simply PsyCap. This PsyCap goes beyond traditionally recognized human and social capital and must meet the scientific criteria of theory, research, and valid measurement. To distinguish from other constructs in positive psychology and organizational behavior, to be included in PsyCap the resource capacity must also be “state-like” and thus open to development (as opposed to momentary states or fixed traits) and have performance impact. The positive psychological resource capacities that meet these PsyCap criteria — efficacy (confidence), hope, optimism, and resilience — are covered in separate chapters. These four resource capacities are conceptually and empirically distinct, but also have underlying common processes for striving to succeed and when in combination contribute to a higher-order, core construct of psychological capital. Besides these four, other potential positive constructs such as creativity, wisdom, well being, flow, humor, gratitude, forgiveness, emotional intelligence, spirituality, authenticity, and courage are covered in Chapters 6 and 7. The concluding Chapter 8 summarizes and presents the research demonstrating the performance impact of PsyCap, the PsyCap questionnaire (PCQ) for measurement and the PsyCap Intervention (PCI) for development. Utility analysis indicates that investing in the development of PsyCap can result in a very substantial return. In total, this book provides the theory, research, measure, and method of application for the new resource of Psychological Capital that can be developed and sustained for competitive advantage.