There is a serious crisis within the social science of psychology. The problem is between non-quantitative psychologists who develop substantive theories of behavior and psychometricians who create the mathematical models to measure behavior. Currently, the two groups are operating in vastly different worlds in the same discipline and their work is diverging farther apart. The inability of the two groups of psychologists to collaborate at the level of theory building and mathematical modelling is impeding the growth of this young science. This book is an attempt to bridge the gap between one substantive area of psychology and psychometrics. Damon Bryant and Larry Davis operationalize some of the key concepts of Flow Theory into the modern information-based framework of Item Response Theory. Within the Positive Psychology framework of Flow Theory, the focus is on challenge, skill, and challenge-skill balance. Within Item Response Theory, the focus is on the item, theta, and theta maximum. The authors lay the foundation for this integration and present several use cases in which the new information-based framework is used to measure constructs and predict important outcomes in fields as diverse as healthcare and American football. This book provides a foundation upon which a fundamental shift can occur in the way that psychological phenomena can be understood in terms of psychometric information. This work is appropriate for anyone looking to understand Flow Theory from a well-grounded quantitative framework. It has immediate applications in healthcare, sports, and work organizations for individuals looking to design flow-based systems to improve human performance.