Externalism about content is the view that the social and / or the physical environment contributes to determining the content of the beliefs of a person. The strongest argument for social externalism derives from the rule-following considerations that motivate a social theory of conceptual content. The best argument for physical externalism goes back to Putnam's twin earth thought experiment. The aim of this paper is to point out that these two sorts of externalism give contradictory accounts of what determines the conceptual content of our beliefs and individuates them. According to physical externalism, the physical environment is sufficient to perform that task owing to suitable causal relations. According to social externalism, the conceptual content of our beliefs is determined by us owing to certain social practices. Possible strategies to reconcile both these accounts are considered.