Consolidation of lawsuits may be ordered by a court when two or more lawsuits involving the same or similar parties (plaintiff and defendant), legal issues, and factual issues are pending in the same court or in different courts in the same jurisdiction (state court system or federal court system). If the lawsuits are pending in different courts one case may be transferred to the other court, and the cases consolidated there.

Laws and rules regarding the consolidation—or transfer and consolidation—of lawsuits vary from state to state and in the federal court system.

In Illinois, consolidation of lawsuits is governed by the Illinois Code of Civil Procedure. The court may order consolidation when two or more actions involving a common question of law or fact are pending before it. This is to promote judicial efficiency and to avoid inconsistent judgments. The decision to consolidate is at the discretion of the court and is typically considered when the cases share similar legal and factual issues, and have the same or related parties. The process is also subject to the rules of the specific court where the cases are pending. If the cases are in different courts within Illinois, a transfer may be necessary to consolidate them in one court. The federal court system has a similar mechanism under the Federal Rules of Civil Procedure, which allows for consolidation when cases involve common questions of law or fact to streamline the process and reduce the risk of inconsistent outcomes.