Adolescence is a period of transition between life as a child and life as an adult. The World Health Organization defines it as from ages 10 to 19. Biologically, entrance into adolescence can be marked by the onset of puberty. Socially, it can be marked by increasing independence from parents; increasing importance of the peer group; and, often, mood swings, conflicts with parents, and risky or reckless behaviours. Adolescence has some universal features, but the nature and even timing of adolescence shows important cultural and historical variations. ‘Adolescence as a life stage’ outlines the evolution of human adolescence and provides anthropological, sociological, historical, psychological, and developmental neuroscience perspectives.