The burgeoning field of positive psychology, which is the scientific study of how individuals and organizations flourish and what makes life worth living, is primarily descriptive and nomothetic. However, it has spawned several prescriptive exercises (i.e., positive interventions) for improving well-being. A common theoretically based definition for a positive intervention does not exist in the current literature. More importantly, although the interventions have shown some success, they have been developed with little thought to theory, such that the mechanisms that make such interventions successful are unknown. The aims of this paper are several-fold: First, I review the importance of theory in general, especially as it pertains to the development and application of positive interventions. Second, to provide a basis for developing good theory, I review criteria that have been proposed for evaluating existing theories and characteristics that differentiate among theories of human behavior and behavior change. Third, I provide an overview of existing behavior and behavior change theories that may be relevant to the development and application of positive interventions, including the Theory of Reasoned Action, the Theory of Planned Behavior, Socio-Cognitive Theory, Trantheoretical Model of Behavior Change, Precaution Adoption Process Model, Health Action Process Approach, Prototype Willingness Model, and Self-Determination Theory. Finally, I propose a new definition of a positive intervention and recommend a theoretical framework for the synthesis and application of positive interventions. Based on this review, I propose a theoretically-based hybrid model, which combines elements of self-determination theory and the health action process approach as a framework for positive interventions moving forward. Altogether, this work sounds a clarion call for the adoption of a rigorous, theory-based, and scientific approach to the design, development, and application of positive interventions.