Abstract: Adolescence is the life-changing phase of human existence that begins as childhood ends and itself is finalized by the onset of adulthood. This chapter sets the stage for the rest of this book by providing an overview of adolescence that includes a review of normal psychosocial stages, adolescent sexual maturity stages, concepts of sexuality, overview of health status of adolescents, and principles of caring for adolescents. Clinicians privileged with the responsibility of caring for youth should serve as advisors of prevention and as committed counselors to guide this precious cargo into the often turbulent times of adulthood. Youth of the second decade of the 21st century will be responsible for caring for the world well into this and perhaps the next century. This book is dedicated to these future ambassadors as they embark on this critical journey.