Parallel litigation is difficult to define and sometimes means what the speaker wants it to mean. It may be limited to identical lawsuits with exactly the same parties and the same claims. It may also mean any instance of two or more lawsuits that may result in claim preclusion for some or all of the parties. It includes concepts of reactive and repetitive litigation, related litigation, and derivative litigation. Whatever it is thought to encompass, it incurs criticism as being vexing and harassing, wasteful of the parties' and courts' resources, and inclined to produce inconsistent results and possibly inter-governmental discord. At the same time, it is a prime example of the long tradition of forum shopping and is a useful tool for the attorney seeking either recovery or protection for the client.

Contradictory policies have also been a problem. Courts' authority and willingness to remedy parallel litigation draws on a number of conflicting doctrines and policies: honoring plaintiff's choice of forum, favoring the first-filed lawsuit, reluctance to dismiss an action that has proper jurisdiction and venue, avoidance of waste, convenience to parties, and respect paid to coordinate courts and governments and, in state-federal conflicts, federalism.

International litigation has the additional problem of the different approaches of the common law and civil law countries. Common law jurisdictions use parallel litigation remedies that favor a multi-factor test and measure detail and nuance, but lack consistency and predictability. Civil law jurisdictions use code-based remedies with more rigid rules and less recognition of special circumstances. Both seem to allow local plaintiffs to manipulate the litigation to a degree that undermines fairness.

The struggle--to define parallel litigation (which cases are parallel enough to justify stopping one?) and deal with its contradictory policies -- is problematic even within the United States. International litigation amplifies the problem, and moreover, amplifies the policy concerns over waste, harassment, and judgment consistency. In the past few decades, treaties and model laws have addressed the issue, with varying approaches and results. This article will examine thirteen of those efforts, commenting on their content, approach, and merits. It will do so against a background of existing remedies under the common law and civil law for international parallel litigation.