Despite the importance of both members of the adult patient–care partner dyad, a majority of research on illness management is focused on the patient or the care partner. The basic principle of the Theory of Dyadic Illness Management is that illness management is a dyadic phenomenon; the theory focuses extensively on the dyad as an interdependent team. The way dyads appraise illness as a unit influences the ways in which they engage in behaviors to manage illness together in a recursive fashion that influences dyadic health. Optimizing the health of both members of the dyad is a goal of the theory. In turn, the health of the dyad can feedback to influence how they appraise and manage illness together. Finally, dyadic illness management is an inherently variable process that is influenced by several contextual factors. Supportive evidence and implications for practice and future research are presented.