Relativism in the philosophy of science is widely associated with the work of Thomas Kuhn and Paul Feyerabend. Kuhn and Feyerabend espoused views about conceptual change and variation of scientific method that have apparent relativistic implications. Both held that scientific theories or paradigms may be incommensurable due to semantic variation. Two ways that truth may be relative because of semantic incommensurability will be distinguished. Davidson’s criticism of the idea of an untranslatable language will be discussed, as well as a response to incommensurability based on the causal theory of reference of Kripke and Putnam. A form of relativism with respect to epistemic rationality may also be derived from the claims of Kuhn and Feyerabend about methodological variation. Kuhn’s initial suggestions about paradigm-dependent standards and absence of extra-paradigmatic standards give rise to a view on which rationality is relative to paradigm. Kuhn’s later view that there is a stable set of shared scientific values is less prone to relativistic interpretation. Feyerabend’s claim that “anything goes” suggests an extreme form of relativism, but should be understood instead as the view that all rules of method may be violated in some circumstances. The latter brings Feyerabend’s view into line with Kuhn’s later view.