This chapter presents an overview of key concepts covered in the subsequent chapters of this book. The book is intended to give an up-to-date overview of what is currently known about neurodegenerative diseases, focusing particularly on Alzheimer’s disease (AD). Current and developing diagnostic tests are described, and the pathological relationships between AD and other conditions now believed to be risk factors for AD are also described. In particular, the book discusses cardiovascular disease, obesity, insulin resistance and type 2 diabetes, focusing on abnormal lipid and sugar metabolism linked to these conditions, and how this is related to AD risk. It provides evidence that improved diet and exercise may reduce AD risk, not just the r...