Adolescence begins with the onset of puberty, defined as the sequence of events by which the child is transferred into a young adult by a series of biological changes. It is during this period that secondary sex characteristics develop. These sex characteristics have been rated into five stages by Tanner and termed Tanner’s sexual maturity rating. Globally, a secular trend is being noticed towards earlier puberty. Arbitrarily, adolescence is divided into three phases: early, middle and late adolescence. Early adolescence refers to 10–13 years, middle adolescence to 14–16 years and late adolescence to 17–20 years. Until recently, the adolescent remained neglected by the medical profession. As a consequence, neither the physician nor the pediatrician cared for his problems. Now, of course, thanks to the concerted efforts of the World Health Organization, and the UNICEF, a worldwide campaign has begun to focus attention on adolescence. According to the Indian Academy of Pediatrics, health problems of children up to 18 years (inclusive) should be the responsibility of pediatricians. Furthermore, the Chapter deals with special features of three stages of adolescence, puberty changes (morphological as well as psychological), factors affecting adolescent health and development, adolescent psychology, adolescent sexuality, adolescent nutrition, special health, medical and psychosocial problems of the adolescent (including anorexia nervosa and bulimia, malnutrition, iron-deficiency anemia), etc. Finally are discussed promotion of adolescent health through such ways and means as health education, life-skill education/skills-based education, counseling for managing stress and emotions, nutritional care and counseling, early diagnosis and management of medical and behavioral conditions and legislation and regulatory policies discouraging risk-taking behavior amongst adolescents.