The present research examines the impact of social identity on prosocial behaviour during middle childhood. A great deal of prior research has evaluated the process of social identity development and its impact on children's intergroup processes. Additionally, children's propensity to behave prosocially has received a considerable amount of empirical attention. However, very little research has been conducted as to how children's social identity can promote or deter intergroup prosocial behaviour. The present studies evaluate the social identity salience of children from 5 to 10-years-old as well as their ability to consider a variety of group related factors when making social judgements. The three prosocial behaviour types used were sharing, helping, and comforting. These behaviours were selected because of their prior use in prosocial research as well as their relevance to children's personal experience. Empathy, perspective taking, and target typicality were also examined in order to better define the relationship in question. The present research involved four studies that included a minimal group paradigm as well as highly salient and well-defined intergroup contexts. The bi-directional potential of the relationship between social identity and prosocial behaviour was also examined through a twelve month longitudinal study. The results indicated that prosocial behaviour was affected by children's social identity. In general, the children were considerably less willing to exhibit prosocial behaviour towards an outgroup than an ingroup member. Furthermore, their prosocial behaviour was related to their ability to empathize with the target. However, in a competitive context, empathy was replaced by perspective taking as a critical factor in their prosocial judgement. Finally, the results differed by age, gender, and behaviour type; suggesting that the relationship between social identity and prosocial behaviour is highly dependent on socio-cognitive development as well as context.