A discussion of the biomarkers of Alzheimer’s disease (AD) first requires a brief historical perspective and an introduction to the disease. This chapter provides a brief outline of AD epidemiology, the definition of an AD biomarker, the classification and features of AD, and AD risk factors, followed by a description of the structure and content of each of the following chapters and their focus on specific types of AD biomarkers. The greatest challenge in AD biomarker research is the ability to diagnose AD and assess prognosis while patients are in the preclinical stages of the disease, before clinical symptoms develop, in order to identify those who would benefit from therapeutic intervention. The importance of diagnosing preclinical stages of AD is presented as a major focus of ongoing research in the field of AD biomarker discovery, development, and validation. A discussion of the societal impact of AD and its associated economic burden to the healthcare system is included at the end of the chapter. This book is intended to provide a comprehensive summary of AD, the rationale for identifying AD biomarkers, and their potential applications in AD diagnosis, prognosis, longitudinal disease tracking, evaluating drug efficacy, and guiding therapeutic intervention.