Mild cognitive impairment is an emerging term that encompasses the clinical state between elderly normal cognition and dementia. Controversy surrounds its characterization, implementation, and definition. Mild cognitive impairment is now the focus of natural history studies, biomarker studies, along with Alzheimer's disease prevention studies. The mild cognitive impairment stage may be the optimum stage at which to intervene with preventive therapies. Depending on the cohort source and definition, between 19 and 50% of mild cognitive impairment individuals progress to dementia (usually Alzheimer's disease) over 3 years. Despite controversy, progress has been achieved in defining risk factors for progression from mild cognitive impairment to dementia. New treatments to prevent development of Alzheimer's disease are targeting mild cognitive impairment as a treatment group and neurologists will increasingly be called upon to make this diagnosis.