© Cambridge University Press 2012. This chapter will provide an overview of the fundamentals of clinical trials in Alzheimer’s disease (AD). A basic understanding of disease biology and clinical presentation is necessary to interpret matters regarding AD trials and we begin with an overview of the disease. We review the goals of AD trials, the basic tools used in their conduct, current and future trial designs, limitations and challenges to trial conduct, and controversies that exist in the field of AD clinical research. The field of AD trials is a rapidly evolving one. We attempt to address recent changes in trial conduct and to consider future changes that will be needed. Introduction to Alzheimer’s disease: Alzheimer’s disease is a progressive neurodegenerative disorder characterized over 100 years ago but still lacking adequate therapies. To date, the US FDA has approved five drugs for the treatment of AD. Most studies suggest that these agents provide only symptomatic improvement in AD and pursuit of treatments capable of altering the natural history of AD is rigorous. Therefore, clinical trials of new therapies in AD in the coming years will continue to be a mainstay of AD research.