This article deals with one of the most controversial topics in practical ethics, namely the inclusion of nonhuman beings into the domain of morality. It seeks to reconstruct Peter SingerÂ’s and Holmes Rolston IIIÂ’s arguments on the value of life and the interests of a moral subject. Both authors hold a widening in the sphere of morality, traditionally reduced to human beings. Their position, however, conflicts with the limits of the moral sphere. While Singer holds that pain and suffering or interests will be the criteria to establish the limits of such domain, Rolston defends that life as a whole should be take into account in ethics. Moreover, while Singer says that only the life of persons, i.e. beings who feel pain and pleasure and who desire and plan their life, is valuable in itself, Rolston maintains that all living beings, even ecosystems and the planet as a whole, have value in itself. This article reconstructs this debate, searching to answer the following question: which are the limits of the moral sphere?