This book summarizes evidence on frailty and ageing, how this may impact patient outcomes and how frailty can be assessed, managed and incorporated in the decision-making process for older patients with cancer.  The book aims to:  empower clinical teams to assess and support older cancer patients with frailty, ideally within a multidisciplinary setting; and to improve the selection of older cancer patients to the most appropriate management/treatment strategies in order to improve the outcomes of this group of patients often underrepresented in research. The reader will learn the methods available for assessing frailty, such as screening tools, but also how to perform different geriatric assessments covering the different key components (physical, nutritional, social, psychological, etc.).