Similar to “parasitism” and “mutualism”, the concept of commensualism defines a kind of biological association, i.e. the neutral interaction between two different species. This paper shows that “commensualism” was initially defined by the Belgian zoologist and parasitologist Pierre-Joseph van Beneden (1809–1894) as referring to biological associations between organic individuals from different species. According to van Beneden, one individual derives biological advantages from this kind of association, whereas the other one remains neutral, i.e. does not receive any biological loss or gain. (...) Tracing the further history of the concept, the paper demonstrates that, while “commensalism” was initially created and used in zoology, it was taken up in other biological disciplines shortly afterward, such as botany and the emerging field of ecology. However, the experimental demonstration of the phenomenon of commensualism remained difficult. This, in turn, contributed to the nomadic existence of this concept in the life sciences of the twentieth century. (shrink)