The now recognized core construct of psychological capital, or simply PsyCap, draws from positive psychology in general and positive organizational behavior (POB) in particular. The first-order positive psychological resources that make up PsyCap include hope, efficacy, resilience, and optimism, or the HERO within. These four best meet the inclusion criteria of being theory- and research-based, positive, validly measurable, state-like, and having impact on attitudes, behaviors, performance and well-being. The article first provides the background and precise meaning of PsyCap and then comprehensively reviews its measures, theoretical mechanisms, antecedents and outcomes, levels of analysis, current status and needed research, and finally application. Particular emphasis is given to practical implications, which focuses on PsyCap development, positive leadership, and novel applications such as the use of video games and gamification techniques. The overriding theme throughout is that PsyCap has both scientific, evidence-based rigor and practical relevance.