Internalism in philosophy of mind is the thesis that all conditions that constitute a person’s current thoughts and sensations, with their characteristic contents, are internal to that person’s skin and contemporaneous. Externalism is the denial of internalism, and is now broadly popular. Joseph Mendola argues that internalism is true, and that there are no good arguments that support externalism. Anti-Externalism has three parts. Part I examines famous case-based arguments for externalism due to Kripke, Putnam, and Burge, and develops a unified internalist response incorporating rigidified description clusters. It argues that this proposal’s only real difficulties are shared by all viable externalist treatments of both Frege’s Hesperus-Phosphorus problem and Russell’s problem of empty names, so that these difficulties cannot be decisive. Part II critically examines theoretical motivations for externalism entwined with causal accounts of perceptual content, as refined by Dretske, Fodor, Millikan, Papineau, and others, as well as motivations entwined with disjunctivism and the view that knowledge is the basic mental state. It argues that such accounts are false or do not provide proper motivation for externalism, and develops an internalist but physicalist account of sensory content involving intentional qualia. Part III critically examines theoretical motivations for externalism entwined with externalist accounts of language, including work of Brandom, Davidson, and Wittgenstein. It dialectically develops an internalist account of thoughts mediated by language that can bridge the internally constituted qualia of Part II and the rigidified description clusters of Part I.