The purpose of this book is to provide a specific group of adults living with intellectual disability, namely Down syndrome (DS), their own unique instrument to assess functional fitness. Previously, individuals living with DS were pooled with individuals living with ID without DS, even though the presence of DS negatively affects functional fitness test performance. The need arose since many adults living with Down syndrome have poor functional ability, live sedentary lives and are overweight or obese. Functional fitness includes parameters such as flexibility, balance, aerobic capacity, functional capacity and muscular strength and endurance. The 14 test items presented in this functional fitness test battery were carefully selected after numerous literature studies and consultations with scholars and specialists who are experienced in working with adults living with DS. Also, extensive pilot studies were conducted in order to select test items best suited to the needs of adults living with Down syndrome. The feasibility, reliability, and validity were determined specifically for adults living with DS. This scholarly book provides an economical and field-based list of test items that can be used to assess, evaluate, and monitor functional fitness. The book aims to contribute to the scientific discourse, reflecting on the functional limitations seen in adults living with DS.