Abstract: We develop a theory of when a deal can be made to stop a state pursuing nuclear weapons, thereby avoiding proliferation or conflict to prevent it. We show a deal can only be made if costly conflict would occur in its absence. Deals are most likely to be made early, when the state’s nuclear program is rudimentary, or late, when it is believed to be nearing success, but not in between. A late deal is credibly enforced by more severe punishment than an early one—immediate conflict rather than merely sanctions—and yet must be more generous to the state. If the state anticipates that a late deal would be offered, it will refuse an early deal in favor of continuing its program to secure the more generous late deal. We test and find support for these predictions against the historical record of deal-making over states’ nuclear programs.