This book provides fundamentals, applications and future directions of several theories of psychology. The first chapter focuses the classification of narcissism and argues multiple parallels between narcissistic behaviors and documented responses to justice threat. Chapter two examines if individuals who report living on following a gluten-free diet adhere across a typical week, and the behaviors involved in adhering to this specific diet. The purpose of chapter three is to study the effectiveness of a best possible physical activity intervention on perceived psychological need satisfaction, well-being, and physical activity. The final chapter examines the nature of the portrayal of African-American women athletes in popular magasines to understand the gendered and cultural messages that are sent about their sport and PA participation.