Adolescence is the transition from childhood to adulthood, a period during which an individual acquires the skills necessary to survive on his or her own, away from parents or other caregivers. Adolescence can be a very confusing time. They experience changes in sleep, diet, mood, weight and attitude and a decreased pleasure from daily activities. These changes are all normal and, in many ways, crucial to healthy adolescent development. Recent research has shown that changes in brain function underlie many of these behavioural changes. These findings have important implications for understanding both normal and abnormal adolescent behavioural patterns, promoting communication between parents and young people, and helping adolescents make the most of their educational opportunities and developing brains. This article discusses the developmental reasons for the consistent behavioural patterns that occur during adolescence and how dramatic changes in brain development and function give rise to these behaviours.