Recent examples of conceptual engineering within the philosophical arena include the proposal by Clark and Chalmers (1998) to extend the traditional understanding of belief, the proposal by Haslanger (2000) to rethink our conceptions of race and gender, and the proposal by Scharp (2013) to reconceive the notion of truth. But there is a good sense in which all philosophical theorizing is at root a form of conceptual engineering, and philosophical attempts throughout the ages to capture the nature of knowledge, evidence, causation, explanation, justice, rights, emotion, consciousness, and so on, count equally as examples. Moreover, examples of conceptual engineering can also be found beyond the confines of philosophy. Indeed, much of scientific theorizing falls under the umbrella of conceptual engineering, as do recent proposals in the social arena to overturn the traditional conceptions of, for example, rape, marriage, and women, where such proposals are largely driven by the desire for social justice and equality. Conceptual engineering has a long history and concerns a wide-ranging and diverse array of topics. Of late, philosophical attention has turned to the nature of conceptual engineering itself. What exactly is conceptual engineering? What unites the diverse array of cases? It will help to distinguish at the outset a broad sense of conceptual engineering from a narrow sense. In the broad sense, conceptual engineering is a form of theorizing that involves a proposed change in linguistic practice. Sometimes this can take the form of a proposal to eliminate the use of a term on the grounds that it is defective in some way, for example by failing to play the explanatory role it was intended to play (e.g. 'phlogiston', 'élan vital'); sometimes it can take the form of a proposal to introduce a new term on the grounds that it is required for explanatory purposes that have not hitherto been recognized (e.g. 'antimatter', 'epistemic entitlement'); and sometimes it can take the form of a proposal to keep a term that is currently in use, but to revise the current use on the grounds that this would constitute some kind of improvement, whether theoretical, practical or normative. Theorizing that involves a proposed change in linguistic practice of any of these kinds-elimination, introduction or revision-is conceptual engineering in the broad sense. But the paradigms of conceptual engineering around which recent debate concerning the nature of conceptual engineering has centred are to be found in that subset of cases that involve the revised use of a term. Each of