People often disagree about what counts as “just” in a particular case. Such disagreement is natural and understandable once we realize that people commonly bring to the concept of justice different understandings of what makes something just or unjust, interpret general principles differently in specific circumstances, and/or fail to see eye to eye on appropriate ways of resolving justice disputes. But in all cases, disagreement about what is just logically requires that the parties share an understanding of what it is that they are disagreeing about. Similarly, any analysis of the role justice might play in a particular domain – here, negotiation – requires a shared understanding of what it is that is playing the role in question. The purpose of this article is to articulate and justify a shared understanding of the concept of justice that facilitates both the understanding and resolution of justice disputes.