Just institutions have claims on us. There are two reasons for thinking that such claims are warranted. First, one may believe that we are under a natural duty of justice to support and further just institutions. If one believes that it matters whether institutions are just, one also has a reason, almost as a matter of consistency, to support and further just institutions. Second, one may believe that by enjoying the benefits brought about by cooperation through just institutions, one incurs an obligation to support these institutions. Those who accept and enjoy the benefits brought about by cooperation through a just scheme are under an obligation of fairness to reciprocate. But what happens to these reasons to support and comply with an institution if the scheme of cooperation is less than fully just? There is hardly a real-world institution, policy, or scheme of social cooperation that would qualify as fully just. However, questions about obligations of fairness and duties of justice under conditions of injustice have hitherto suffered relative neglect. I shall outline an overall framework for thinking about these questions by asking what the victims of injustice owe to moderately unjust institutions.