Maintaining an ideal weight throughout life is the most beneficial thing someone can do for their body. A healthy body and ideal weight can be achieved with proper nutrition and lifestyle, starting from childhood and even infancy. Therefore, it is important for those raising children to be conscious of this issue and to be good role models and guides for their children by exhibiting the healthiest lifestyle habits. We know that it is almost impossible to remove excess fat tissue acquired during childhood from the body at later ages. Body fat accumulation is usually evaluated by body mass index (BMI), which is calculated using weight and height proportions. BMI is an effective and useful tool for both people and healthcare professionals to track body fat percentage. However, when monitoring body fat with BMI special adjustments need to be made in children, the elderly, different genders, and individuals with high muscle mass. This book provides a comprehensive overview of BMI as a screening measure.