Successful communication is a key determinant of positive outcomes in a wide array of areas, and is therefore one of the most important human social functions. Despite this, research rarely considers the social dynamics involved in communication, instead focussing on the process at an individual level. The present thesis therefore employs social identity theory to determine when and why communication outcomes are successful in some contexts, but not others. Specifically, the current research seeks to explore why communication between those with whom we share a social identity – ingroup members – is generally more effective than with those with whom we do not share a social identity – outgroup members. An online communication paradigm was developed in two experiments to achieve this. In the first study, participants (N = 237) read either a high quality or low quality set of Lego instructions said to have been created by either an ingroup or outgroup member, and indicated which of four pictures showed the correct model based on the instructions. The second study (N = 306) followed the same procedure, however participants were told that the instructions were created by either an ingroup, close outgroup, or distant outgroup member. Contrary to predictions, participants in the first study were no better at recognising the correct model regardless of instruction source or instruction quality. This lack of effects was attributed to a weak manipulation of group identity and a ceiling effect on the focal DV. In line with predictions, participants in the second study scored better when receiving instructions ostensibly provided by either an ingroup or close outgroup member, as opposed to a distant outgroup member. These findings not only suggest that social identity is an important determinant of communication outcomes, but also provides a novel insight in showing that group similarity moderates the effect.