This chapter presents an overview of aging and introduces the reader to the demographics of the older population that includes present size, projected growth rate, current health status, and patterns of medication use, both prescription and over-the-counter drugs and supplements, in community-dwellers and those in assisted living/nursing homes. Additionally, it supplies essential information on the type and quality of evidence (randomized clinical trials, observational studies, systemic reviews, and meta-analyses) referenced throughout this book.