The Carnegie Corporation of New York made a critical grant to Princeton University to strengthen the Iran nuclear agreement. A central obstacle to a successful agreement was Iran’s Arak heavy-water reactor. In April 2014, the Princeton University Program on Science and Global Security (PSGS) team suggested a redesign of the reactor core making it impossible to produce weapons grade nuclear material. The research PSGS did on this was communicated directly to leaders and negotiators in Washington, D.C. and Tehran. Shortly thereafter, Iran made a proposal to significantly lower plutonium production at the reactor by redesigning it along the lines recommended by PSGS. The unique work supported by Carnegie brought the P5+1 and Iran closer to an agreement by resolving a key technical hurdle.