This dissertation analyzes and develops the ethical dimension of the Eucharistic theology of the Eastern Orthodox theologian John Zizioulas. I argue that though Zizioulas is criticized for eschewing traditional accounts of ethics, his work has profound implications for how Christians can fruitfully engage with our pluralistic society without resorting to sectarianism or sacrificing their particular convictions. The project begins by examining Zizioulas’s claims concerning divine and human ontology in order to understand his contention that the Kingdom of God is an ontological, rather than moral, reality. This emphasis on existential concerns has led some to claim that Zizioulas’s theology makes morality all but superfluous. On the contrary, I argue that morality plays a crucial role in Zizioulas’s theology insofar as morality is reconceived in terms of penitence. For Zizioulas, ethics is a matter of recognizing and taking responsibility for the sins of the world as a pre-requisite for participation in the Kingdom of God made manifest in history by the event of the Eucharist. In this way Christian ethics retains its particularity insofar as it is intimately related to the Eucharist and the eschaton, and yet it is also compatible with pluralism insofar as repentance does not require belief or participation in Christianity.