Conceptual engineering is the method for assessing and improving our representational devices. On its ‘broad‐spectrum’ version, it is expected to be appropriately applicable to any of our representation‐involving cognitive activities, with major consequences for our whole cognitive life. This paper is about the theoretical foundations of conceptual engineering thus characterised. With a view to ensuring the actionability of conceptual engineering as a broad‐spectrum method, it addresses the issue of how best to construe the subject matter of conceptual engineering and successively defends the theses that conceptual engineering should be: (i) About concepts, (ii) psychologically theorised, (iii) as multiply realised functional kinds. Thereby, I claim to theoretically secure and justify the maximum scope, flexibility, and impact for the method of conceptual engineering on our representational devices in our whole cognitive life—in other words, a broad‐spectrum version of conceptual engineering.