I wish to share some recent work in progress around a theory of by-production. My starting hypothesis is that the mode of existence of certain concrete and theoretical objects can be comprehended only if we regard them as by-products, that is, as lateral effects of processes geared to produce something else. While recent and not-so-recent ecological thought brought the value of by-products to the fore, for instance in centering the importance of up-cycling, by-production as a distinctive regime of practice is still under-theorized. Mine will thus be an effort to contribute to this task against the backdrop of two sets of open problems in contemporary critical discourse: first, the troubled relation between production and reproduction, ongoing in materialist and feminist debates; and secondly, the emphasis on undoing that, while making possible a number of crucial intellectual and political gestures (often expressed by the prefix de-: e.g. de-construction, de-identification, de-colonization, de-toxification), risks to incur in the aporia of negative action. By-production could offer a way to sidestep some of these issues and make available a different ethical-aesthetical horizon.