Positive Work and Organizations (PWO) continues to permeate organizations that desire to improve employee optimal functioning. One aspect of PWO includes positive psychology interventions (PPI’s) at work, which uses the theory and scholarship of positive work and organizations to design interventions aimed at improving employee work outcomes. A recent systematic review and meta-analysis by Donaldson, Lee, and Donaldson (under review) found a link between PPI’s at work and improving desirable and reducing undesirable work outcomes. The purpose of this chapter was to synthesize the empirical evidence demonstrating the efficacy of these interventions using a theory-driven evaluation (TDE) approach. TDE refers to the systematic use of substantive knowledge (i.e., social science theory, stakeholder theory, or some combination of both) about the intervention under consideration to improve, produce knowledge, or determine its merit, value, and worth (Donaldson, 2007). We found that positive psychology theories, intervention delivery methods, types of participants, and contexts in which these interventions are implemented determines the efficacy of their outcomes. The findings will have implications for enhancing the effectiveness of future interventions as well as provide valuable information for practitioners deciding to use PPI’s in their organizations.