This is the official guidebook complied by the Japan Diabetes Society for diabetes patients and their families. It has been revised over many years with the goal of transmitting knowledge related to diabetes. It is designed to help people control diabetes and lead complication-free and fruitful lives. It contains the latest information based on the rapid progress in knowledge of the causes of diabetes and techniques for treatment. It brings together a wide body of content, including basic knowledge, prevention and treatment of complications, mental health, and guidance for diabetes life. It also deals with psychological problems and the issue of diabetes in the elderly.