With the new wave of claims against corporations for human rights violations – particularly in the context of aiding and abetting government abuse – there are unusually difficult problems of joint tortfeasor liability. In many circumstances, one tortfeasor – the corporation – is a deep-pocketed defendant, easily subject to suit, but only marginally involved in the unlawful conduct. Another tortfeasor – the sovereign – is a central player in the unlawful conduct, but, with limited exceptions, is immune from suit under the Foreign Sovereign Immunities Act. A third tortfeasor – the low-level security personnel – accused of actually committing the atrocity, is beyond the jurisdictional reach of the forum and is an insolvent, judgment-proof defendant. How should an adjudicator apportion responsibility among these joint tortfeasors? Does it matter that the principal players are immune or insolvent, while the marginal player is not? In apportioning responsibility, is it relevant that one tortfeasor simply knew of the misconduct or was negligent with respect to its likely occurrence, although it did not intend for the violation to occur? Despite the saliency of these questions, international law does not provide the answers. These problems are only exacerbated by the fact that international law violations can be pursued in multiple arenas – in national courts, international tribunals, and international arbitral bodies. As a general rule, international tribunals will resolve the question of apportioning liability using public international law, while domestic courts will resolve the question by recourse to private international law, and arbitral panels will rely on the governing law of the contract. The approach for resolving questions of apportionment will differ in these contexts, although each will resort to domestic tort law in one way or another.