This chapter discusses physical, cognitive, and social development during adolescence. It covers 5 main learning goals: 1) the nature of adolescence, 2) changes during puberty and to the brain and sexuality, 3) health problems adolescents face, 4) cognitive changes, and 5) how schools influence development. Key topics include pubertal changes, brain development, adolescent health issues like substance abuse and eating disorders, cognitive changes according to Piaget's stages, and challenges of transitioning to middle/high school. The chapter provides classroom activities, lecture suggestions, videos and references to help teach about physical and mental development during the transition to adulthood.