As children become teenagers, their bodies change dramatically. An obvious change is the growth spurt, but the young person also becomes reproductively mature and there are significant neural and cognitive changes. ‘Puberty—body and brain changes’ asks why puberty happens and considers the variations in the onset of puberty, the impact of puberty, and the consequences of early, on-time, and late puberty. Does the timing of puberty matter? The changes in the brain at adolescence are also considered. Advances in neuroimaging techniques have facilitated extensive brain studies. The remodelling of the brain in adolescence has been related to a number of aspects of cognitive and social functioning.