Parallel litigation

Parallel litigation is a scenario in which different courts are hearing the same claim(s). The federal courts have a policy of not hearing (abstaining from) a case when there is parallel litigation going on in state courts, following the [Colorado River abstention] doctrine. In that case, the federal government sued for adjudication of certain water rights in Colorado; parties to a state court proceeding joined the U.S. as a defendant, and the Supreme Court said the federal courts should defer to that parallel litigation.