There is a need to understand how close relationship partners affect one another’s health outcomes through their health behaviors. To fill this gap, we present the Dyadic Health Influence Model (DHIM). The DHIM identifies three paths through which one relationship partner (the agent) can affect the health beliefs and/or behavior of the other partner (the target): (1) the agent’s health-relevant behaviors (health behavior transmission path), (2) the agent’s and target’s relationship-based beliefs and behaviors (relational behaviors path), and (3) the intentional influence the agent uses (influence strategies path). A central premise of the model is that agents’ behaviors result not only from their beliefs about targets’ health, but also from their beliefs about targets and their relationships. We incorporate theory and empirical research to provide initial support for the DHIM paths and identify novel hypotheses that can be derived from the model. Finally, we discuss important moderators of these paths.