The clinical features of periodontal diseases in children and adolescents differ from those in adults. Periodontitis is extremely rare in children, except those complicated with certain kinds of systemic diseases, whereas gingivitis is commonly encountered. Childhood gingivitis can be reversed by professional mechanical tooth cleaning in combination with tooth brushing instruction. Other types of periodontal diseases include gingival recession, which is mainly caused by traumatic occlusion, and gingival overgrowth, which has a hereditary background and is associated with specific medication such as antiepileptic phenytoin. This book presents and discusses periodontal disease in children and adolescents.