In three experiments, we investigated the spontaneous attention of perceivers to the nature of targets' facial expressions, specifically whether they were displaying an enjoyment or a non-enjoyment smile. Further, we investigated the social functions of sensitivity to smile type and the consequences of such sensitivity for subsequent interactions. Results demonstrated that perceivers did indeed spontaneously attend to smile type, especially in situations where issues of trust or cooperation were made salient. Further, this sensitivity had an impact both on the evaluations of the target individuals and the cooperative behaviour of individuals towards those displaying enjoyment and non-enjoyment smiles. Participants evaluated individuals displaying enjoyment smiles more positively than those displaying non-enjoyment smiles and had higher rates of cooperation with those displaying enjoyment smiles. These results are discussed in terms of the social functions of facial expressions.