This chapter provides a comprehensive exploration of psychological theories and models that inform the design and implementation of effective global health interventions. It examines key frameworks, including the Health Belief Model, Transtheoretical Model, Theory of Planned Behavior, Social Cognitive Theory, and Self-Determination Theory, highlighting their role in understanding, predicting, and shaping health-related behaviors. Additionally, the chapter discusses Prospect Theory, Nudge Theory, and Cognitive Behavioral Theory, offering insights into decision-making, risk perception, habit formation, and behavior modification. By integrating these models, the chapter illustrates how psychology contributes to evidence-based public health strategies that address challenges such as vaccine hesitancy, chronic disease management, and mental health promotion. Through real-world case studies, it demonstrates how these frameworks are adapted across diverse cultural and systemic contexts, ensuring that interventions are both scientifically sound and socially relevant. Beyond theoretical discussion, this chapter emphasizes the practical application of psychological insights in global health, equipping readers with a robust toolkit for designing culturally sensitive, behaviorally informed health strategies. By bridging theory and practice, it underscores the critical role of psychology in promoting health equity, improving health outcomes, and supporting sustainable, interdisciplinary solutions to global health challenges.