The main objective of this book is to show that Porphyry extends moral concern to harmless living beings in his account of justice in On abstinence. It is argued that while Porphyry shares some commonalities with the Platonists, Stoics and Theophrastus on the nature of justice, he develops an original notion of justice also attributing it to external actions. As an attribute of actions, justice consists in refraining from harming harmless animate creatures including animals and plants. Porphyry’s account is entangled with his polemic with opponents of vegetarianism and his quotations from other authors in that polemic. By unravelling these inner complexities of the treatise, this book shows the surprising modernity of his discussions.