Older adults in the United States have lower rates of mental health care utilization than young adults. To understand these lower rates of mental health care, we performed a systematic review, in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, of barriers that prevent older adults from seeking and accessing treatment. We searched PubMed, PsycINFO, and Clinical Key to identify studies of barriers to mental health treatment in the older adult population (in individuals 50 y of age and older). Thirty-two articles met inclusion criteria (English language and focused on barriers to care in older adults) and exclusion criteria (focus on non-United States populations, focus on younger adults, or no focus on barriers to care). We identified 5 categories of barriers to mental health care in older adults: (1) attitudes and knowledge among older adults; (2) comorbid medical conditions; (3) provider-related factors; (4) other extrinsic barriers (eg, cost, transportation, reliance on caregivers); and (5) unique factors that affect older adults in minority populations. Large studies have primarily identified intrinsic barriers, including negative attitudes toward mental health care and lack of perceived need for treatment, as preventing older adults from seeking mental health care. Minority populations have also been found to face cultural barriers and increased levels of stigma compared with non-Hispanic whites, although several of the identified articles concerning barriers among minority older adults involved qualitative studies with small samples. Larger quantitative studies may help clarify the relative importance of barriers affecting this population. Interventions that have been shown to increase access to mental health services for older adults include community-based care and integrated primary and psychiatric care, but these strategies can be difficult to implement in low-resource settings. More research is needed to determine which interventions and policies are most effective in targeting particular barriers.