Cognitive impairment is a frequent complication in Parkinson's disease (PD), though it can be heterogeneous in its presentation and progression. Cognitive deficits vary among patients with regard to clinical features, severity, and progression to dementia. A growing recognition of cognitive impairment in PD in both the clinical and research settings has led to advances in diagnostic criteria and improved understanding of the clinical phenotypes, associated biomarkers, and underlying pathophysiology of both PD dementia and PD mild cognitive impairment. Therapeutic interventions are geared to improve symptoms and ideally to prevent cognitive decline. Here the authors summarize the current research on the characterization of cognitive impairment in PD, with specific attention focused on its clinical phenotype, associated neuropsychiatric and prodromal features, pathological changes, genetic variations, and imaging and biochemical biomarkers.