This essay argues that fairness can be understood as appropriate concession in the context of a cooperative endeavor, and then explores why questions of fairness often give rise to disagreement. A constructivist theory of judgments of fairness is proposed according to which they are grounded, ultimately, in a motivational disposition to make and seek concessions in cooperative contexts when others are similarly disposed. It is argued that when judgments of fairness are interpreted in this way, issues of fairness will often admit of reasonable disagreement, in the sense that incompatible judgments can be supported by reasoning that is fully competent. Two different senses of the reasonable are distinguished, and the possible epistemic relevance of this distinction is noted. The essay concludes with an argument that the divergence of competently reasoned judgments of fairness envisaged by the theory should not be understood as relativism about fairness.