Neurodegenerative diseases, in particular Alzheimer' s disease, represent significant unmet medical needs due to a lack of effective therapeutic treatment options and cause a substantial burden for health care systems. Accumulation of β-amyloid peptides within the brain is believed to be an initial trigger of the disease process. In the last 20 years, immunotherapy has emerged as a promising target-directed strategy to develop efficient treatment options with disease-modifying potential. Unfortunately, either active vaccination against β-amyloid or its fragments, as well as passive immunization using monoclonal antibodies, have largely failed to show a clinical benefit in a variety of clinical trials. This chapter addresses progress and developments with regard to active and passive immunization against Aβ and summarizes the current state of clinical trials.