There are a wide range of roles and effects that justice can have in negotiations at the international level. It can be a source of conflict and trigger for negotiation, a referent guiding negotiations, a subject of negotiation, a tool to reach effective agreements, and a tactical tool. Justice can assume any or several of these roles in any one negotiation. This article looks at justice as a lens through which to understand what drives negotiation processes and explains different results in the international arena.