We now know that the onset of the pathological processes leading to Alzheimer’s disease (AD) may be 15–20 years before symptoms appear. This focuses attention on synaptic changes and the early role of tau, and less on the hallmark amyloid plaques (Aβ) and neurofibrillary tau tangles. Sensitive biomarkers to allow early screening will be essential. Familial autosomal AD is the result of mutations in one of three genes (APP, PSEN1, or PSEN2), each directly related to increased Aβ, and informs pathological mechanisms in common sporadic cases, but are also subject to influence by many risk genes and environmental factors. The essential role of apolipoprotein E in neuronal repair and Aβ clearance provides a therapeutic target but also a challenge in carriers of the risk gene APOE4. Current treatments are symptomatic, derived from neurotransmitter deficits seen; particularly cholinergic, but emerging data suggest alternative targets which may prove more productive.