Evidence of beta-amyloid plaques can be found in the brains of people up to 20 years prior to the onset of cognitive impairment due to Alzheimer’s disease and yet, some people with beta-amyloid plaques will never develop Alzheimer’s. Abnormal tau protein starts to appear in neurofibrillary tangles in the brain later but still at least several years before the onset of cognitive impairment. Information from amyloid and tau PET scans as well as new blood tests for beta-amyloid and tau have confirmed this timeline. A recent paper shows how it might be possible to identify research subjects who are in this narrow window, those who currently have amyloid but no tau, but who have characteristics suggesting that they will become tau-positive and cognitively impaired within five years.