The design is an open-ended, prospective, observational, (non-interventional) registry for subjects with mild cognitive impairment (MCI), early symptomatic Alzheimer's disease, Alzheimer's disease, or dementia with clinical suspicion of Alzheimer's disease under the care of a neurologist, psychiatrist, geriatrician or other qualified provider. Longitudinal data are collected from subjects, their care partner(s), and their treating healthcare provider during routine clinical encounters using a structured and standardized data collection method. Approximately 2,000 subjects, with no defined upper limit, across around 75 clinical sites worldwide will be recruited.