The immune system plays a significant role in Alzheimer disease (AD). β-Amyloid deposition in the cortex is thought to be an initiating event in AD and the widely believed amyloid hypothesis proposes removal of amyloid may delay disease progression. Human trials of active or passive immune agents have failed to show benefit and increased adverse events of vasogenic edema and microhemorrhages. Evidence suggests the illness may be too advanced by the time patients are symptomatic with dementia. Future directions include better understanding of how and where immunotherapies should be targeted and treating patients at earlier stages of the illness.