Have you ever seen the magnificent spectacle of males trying to impress a female or intimidate other males? Then you probably have noticed the huge variation in courtship towards the chosen one or in aggression towards rivals! Individual differences in behaviour are widespread in the animal kingdom and strongly influenced by the social environment during development. Yet by which mechanisms does the social environment influence adult behaviour and what aspects of behaviour are affected? We studied the effects of the social environment on the frequency and type of social interactions, sexual maturation and physiology during development. Male zebra finches (Taeniopygia guttata) were observed during adolescence in mixed-sex pairs, mixed-sex juvenile groups, and mixed-sex mixed-age groups. When they were adult, their courtship and aggressive behaviour was compared. We found that group-reared males had more social interactions and a more rapid sexual maturation than pair-reared males. Interestingly, intense agonistic behaviour only occurred in mixed-age groups. As adults, males reared in juvenile groups sang more to females than pair-reared males. All males courted single females more than those with a mate, but group-reared males discriminated more. Furthermore, group-reared males showed more aggression, especially towards males, whereas pair-reared males chased less and discriminated less. In conclusion, an enriched social environment during adolescence leads to an increased frequency of social interactions, which seems to stimulate sexual maturation and bring about more discriminating courtship and competitive strategies. Courtship strategies are also modified by experiences with adults. To demonstrate the adaptive significance of the different behavioural strategies, reproductive success of these birds should be investigated under different social conditions.