In this chapter, we first trace the history of the concept of ecological niche and see how its meanings varied with the search for a theory of ecology. The niche concept has its roots in the Darwinian view of ecosystems that are structured by struggle for survival and, originally, the niche was perceived as an invariant place within the ecosystem, that would preexist the assembly of the ecosystem. The concept then slipped towards a sense in which the niche, no longer a pre-existing ecosystem structure, eventually became a variable that would in turn have to be explained by the competitive exclusion principle and the coevolution of species. The niche concept used at that time, while more operational from an empirical point of view than the previous one, suffered however from an ill-founded definition. A recent refoundation by Chase & Leibold enabled to overcome some of the definitional difficulties.We then present how, in contemporary ecology, the niche concept is recruited to explain biodiversity and species coexistence patterns. We show how, in parallel, neutralist models, by succeedingly explaining some ecological patterns without resorting to explanations in terms of niche, have questioned the explanatory virtues of the niche concept.In conclusion, it seems that the forunes and misfortunes of the niche concept can be seen as a reflection of the difficulties of ecology to give birth to a theory that would be both predictive and explanatory.