This chapter provides an extensive review of Alzheimer’s Disease, covering its etiology, genetics, and the central role of protein misfolding and proteostasis. It details the Amyloid-β aggregation pathways and associated pathogenic mechanisms, such as mitochondrial dysfunction and oxidative stress. The discussion extends to current diagnostic landscapes, including the A/T/N classification in CSF and blood, and introduces ultrasensitive technologies like SIMOA. Finally, the chapter reviews immunotherapeutic advancements, focusing on monoclonal antibodies in clinical trials and the development of camelid-derived single-domain antibodies (nanobodies) for the targeted neutralization of toxic Aβ oligomers.