Adolescence (10-19) is a phase of life which has recently gained recognition as a distinct phase of life with its won special needs. This phase is characterized by acceleration of physical growth and, psychological and behavioral changes thus bringing about transformation from childhood to adulthood. This chapter on adolescence aims at generating an understanding of what is special about adolescence and provides and overview of important matters concerning adolescent health and development. It examines the perceptions of adolescents and of adults regarding adolescents’ health concerns and explores the rationale for investing is adolescent health. This module is a foundation for all the subsequent modules wherein issues pertaining to adolescent health and development have been dealt with in greater depth.