During the past two decades the prevalence of overweight and obesity in children has increased rapidly world-wide. Together with the rising of childhood obesity, some adult-like metabolic disorders, such as the impairment of insulin sensitivity or hypertension, have become apparent already among school-aged children. As both a consequence and a contributor to the childhood obesity, the low-level physical activity of children, especially in the westernised societies, warrants attention. This book examines the value of physical activity in preventing and combating childhood obesity and its metabolic comorbidities.