This is a critical study of the Incommensurability Thesis of Thomas Kuhn and Paul Feyerabend, that different scientific theories may be incommensurable because of conceptual variance. While critical of the thesis and of the arguments for it, the author aims to acknowledge the views of his opponents. This study develops a version of the standard "referential" response to the thesis that conceptually variant theories may be comparable by means of referential overlaps of their terms. A modified causal theory of reference is adopted, which allows a reference-determining role to descriptions and reference-fixing to occur after original baptisms. On this basis, it is argued that there may be failure of translation between the sub-languages employed by theories. The claim that theories may fail to be translatable is defended against Davidson and Putnam"s thesis that the idea of untranslatability is incoherent. It is also argued that the thesis of translation failure between theories can be maintained on the basis of a realist commitment.