Suppose you could change people's way of thinking about the world at its very roots, by changing the very concepts by means of which they think. Suppose, further, that this would make the world a better place; that would be quite something. Knowledge and Conceptual Engineering is a comprehensive and systematic study of the nature and normativity of conceptual engineering. This book comprehensively deals with all the central questions in the field: the very possibility of conceptual engineering, its success conditions, the epistemic and moral permissibility of conceptual engineering, the nature of conceptual ignorance and conceptual understanding, and duties to engage in conceptual engineering. It also considers the political aspects, such as engineering social kind concepts, the nature of hermeneutical injustice, and conceptual disinformation. Mona Simion and Christoph Kelp develop a systemic and unified framework centred on conceptual functions, and espouse a functionalist approach that is wholeheartedly optimistic, in that it takes conceptual engineering to be something that we can and should do.