Frailty represents an important challenge for aging populations. As a concept it is full of ‚known unknowns‘ such as which mechanisms lead to frailty and how it is best managed. In order to examine these circumstances, the new science of understanding and managing frailty requires an appropriate framing of the problem. This publication investigates the biology and management of frailty and its social aspects. It considers these and related questions: How can we recognize frailty? How does an understanding of frailty increase our comprehension of the aging process? What are its implications for health care systems, including primary care, hospitals and rehabilitation? How will a growing number of frail older adults affect society more generally? The book focuses on frailty as a state of vulnerability, which is related to aging, but which can occur across the life course, and aims to improve the life of frail people and those around them. The book is highly recommended to researchers in aging, health science researchers, health care professionals and anyone interested in the understanding of the aging process.