This chapter examines the neurodevelopmental changes that define adolescence, challenging the notion that teenage behaviour stems purely from hormonal changes. It frames the adolescent brain as undergoing significant reconstruction, with maturation progressing from the “reptile brain” (brainstem) and “monkey brain” (limbic system) to the “evolved brain” (cerebrum). Critically, while the limbic structures governing emotion, reward, and risk-taking—including the nucleus accumbens and amygdala—develop early, the prefrontal cortex responsible for impulse control, decision-making, and empathy lags behind, not fully maturing until the mid-twenties. This developmental mismatch explains many characteristic adolescent behaviours: impulsivity, emotional intensity, reward-seeking and poor risk assessment. The chapter highlights how synaptic pruning (“use it or lose it”) and myelination shape neural pathways during this period, with environmental experiences playing a crucial role. The chapter also illuminates concerns related to how today’s screen-dominated environment may negatively impact this critical developmental window, potentially interfering with healthy brain maturation in ways previous generations never experienced.