BACKGROUND: The increased "outsourcing" of care-related tasks to patients and their informal caregivers is part of a broader trend in service industries toward engaging customers as "coproducers" of service outcomes. As both quasi-patients and quasi-providers, caregivers may play a critical role in successful coproduction, but they require coordination with care providers to play this role effectively. When tasks are highly interdependent, uncertain, and time constrained, as they often are in health care, relational forms of coordination are expected to be most effective. PURPOSES: This study explores the effects of coordination between formal providers and informal caregivers on caregiver preparation to provide care at home and the effect of caregiver preparation on patient outcomes. Gittell's theory of relational coordination posits that effective coordination occurs through frequent, high-quality communication that is supported by relationships of shared goals, shared knowledge, and mutual respect. We extend the relational coordination model, previously used to examine coordination between formal providers, to encompass coordination of care between formal providers and informal caregivers. METHODOLOGY: We surveyed patients before and 12 weeks after knee replacement surgery to assess outcomes. At 6 weeks postsurgery, we surveyed their caregivers regarding coordination with providers and preparation to provide care. FINDINGS: We found that relational coordination between formal providers and caregivers improves caregiver preparation to provide care, which, in turn, is positively associated with patients' freedom from pain, functional status, and mental health. IMPLICATIONS: Providers should be encouraged to attend to the interpersonal aspects of their interactions with caregivers to promote relational coordination, which may ultimately benefit the patient's health. It is not enough, however, to urge providers to build shared goals, shared knowledge, and mutual respect with patients and caregivers. Dedicated resources and support are needed, given the context of constrained resources and brief encounters in which providers deliver care.