This chapter considers the spectrum of Alzheimer’s disease (AD) presentations, from preclinical stages, through the prodromal mild cognitive impairment (MCI) stage, and the dementia stage. AD is named after Alois Alzheimer, a German neuropathologist and psychiatrist, who described the first case of AD dementia in 1906. After her death, Alzheimer studied her brain’s histopathology, reporting what is considered the hallmark pathology of AD – beta-amyloid plaques and neurofibrillary tangles. In 2010, with growing understanding that AD has a long preclinical and prodromal process, workgroups convened by the National Institute on Aging (NIA) and the Alzheimer’s Association (AA) updated criteria for dementia due to AD, as well as creating criteria for the symptomatic predementia phase of AD, and the asymptomatic preclinical phase. MCI has become the preferred term for patients in the prodromal stage of AD. The NIA-AA workgroup diagnostic criteria are the first specifically referring to MCI due to AD.