IMPORTANCE: Cognitive decline is a common and feared aspect of aging. Mild cognitive impairment (MCI) is defined as the symptomatic predementia stage on the continuum of cognitive decline, characterized by objective impairment in cognition that is not severe enough to require help with usual activities of daily living. OBJECTIVE: To present evidence on the diagnosis, treatment, and prognosis of MCI and to provide physicians with an evidence-based framework for caring for older patients with MCI and their caregivers. EVIDENCE ACQUISITION: We searched PubMed for English-language articles in peer-reviewed journals and the Cochrane Library database from inception through July 2014. Relevant references from retrieved articles were also evaluated. FINDINGS: The prevalence of MCI in adults aged 65 years and older is 10% to 20%; risk increases with age and men appear to be at higher risk than women. In older patients with MCI, clinicians should consider depression, polypharmacy, and uncontrolled cardiovascular risk factors, all of which may increase risk for cognitive impairment and other negative outcomes. Currently, no medications have proven effective for MCI; treatments and interventions should be aimed at reducing cardiovascular risk factors and prevention of stroke. Aerobic exercise, mental activity, and social engagement may help decrease risk of further cognitive decline. Although patients with MCI are at greater risk for developing dementia compared with the general population, there is currently substantial variation in risk estimates (from <5% to 20% annual conversion rates), depending on the population studied. Current research targets improving early detection and treatment of MCI, particularly in patients at high risk for progression to dementia. CONCLUSIONS AND RELEVANCE: Cognitive decline and MCI have important implications for patients and their families and will require that primary care clinicians be skilled in identifying and managing this common disorder as the number of older adults increases in coming decades. Current evidence supports aerobic exercise, mental activity, and cardiovascular risk factor control in patients with MCI.