Two questions are addressed in this essay: (1) Is polarization understood differently in international relations, as compared to domestic politics? (2) How does domestic polarization affect diplomacy and the conduct of international relations? In the international context, polarization traditionally has been understood primarily in terms of power balances rather than irreconcilable conflict, as in the domestic context. A new kind of bipolarity, which combines aspects of power with irreconcilable identities and objectives, seems to be emerging: democratic versus autocratic states. Domestic polarization has several spillover effects on diplomacy in today's world. The inability to compromise at home becomes the modus operandi in the international arena. Domestic polarization stands in the way of effective cooperation on burning global issues, entails obvious risks that the venerable norm pacta sunt servanda will be violated, and undermines the sense of common domestic purpose that is usually perceived to strengthen diplomacy.