Objective: The goal of this review was to assess the relationships among aims, designs, and outcomes of integrated inpatient medical and psychiatric care units (IMPUs) and gather the evidence base on the effectiveness of these units. Methods: Using online searches of Embase, Medline, Web of Science, PsycINFO, Scopus, CINAHL, Cochrane, and Google Scholar, the authors identified and reviewed literature describing the aims and outcomes of specific IMPU designs. Results: The search yielded 55 studies, in which the authors identified 39 IMPUs that focused on patients with mood, psychotic, somatic symptom, substance use, organic, and personality disorders and a broad array of medical diagnoses. Most units were psychiatric-medical units and had medium medical and psychiatric acuity capabilities. The studies reviewed provided little information on the cost-effectiveness of various IMPU designs. Although some comparative studies indicated reductions in hospital length of stay (LOS), these studies were generally of low quality and rarely reported other intended outcomes. Conclusions: IMPUs may help shorten LOS. IMPUs should focus care on patients with complex conditions and high acuity to maximize health system value. Implementing compulsory admission facilities; qualified psychiatric, medical, and nursing staff involvement; and cross-disciplinary training may improve IMPUs’ capacity to treat high-acuity patients. Future research should relate IMPU designs to intended outcomes.