Sanford Goldberg argues that a proper account of the communication of knowledge through speech has anti-individualistic implications for both epistemology and the philosophy of mind and language. In Part I he offers a novel argument for anti-individualism about mind and language, the view that the contents of one's thoughts and the meanings of one's words depend for their individuation on one's social and natural environment. In Part II he discusses the epistemic dimension of knowledge communication, arguing that the epistemic characteristics of communication-based beliefs depend on features of the cognitive and linguistic acts of the subject's social peers. In acknowledging an ineliminable social dimension to mind, language, and the epistemic categories of knowledge, justification, and rationality, his book develops fundamental links between externalism in the philosophy of mind and language, on the one hand, and externalism is epistemology, on the other.