Retaining human immunodeficiency virus (HIV)-infected patients in medical care at regular intervals has been shown to be linked to positive health outcomes. This article examines the available literature and research on retention and engagement in care of HIV-infected patients. We identify the extent of the problem of keeping patients engaged in care, as well as analyze which groups of patients are likely to be lost to follow-up. A review of different ways to measure patient retention is considered, as well as some preliminary data that suggest successful ways to re-engage patients in care. The need to ensure that HIV-infected patients are retained in care is a pressing public health issue and one that affects multiple populations. Further research and exchange of information are needed to keep patients in continuous care and to ensure that all patients are provided with regular, high-quality care that achieves both desired patient and population health outcomes.