Discovery is the factfinding process in civil litigation in which the parties to a lawsuit exchange requests for the production of documents and other tangible items (requests for production); written questions to be answered under oath (interrogatories); witness testimony to be provided by oral deposition; disclosures that may be required under the applicable rules without request from an opposing party; and requests or subpoenas to third-parties (who are not parties to the lawsuit) for the production of documents or tangible things, or the giving of testimony by oral deposition, for example.

The discovery process is one of the most important, time-consuming, and often expensive parts of civil litigation. The discovery process—including the scope of discovery requests, deadlines to respond, and privileges from responding—are usually governed by the state or jurisdiction’s rules of civil procedure or code of civil procedure. For example, in federal court discovery is governed by the Federal Rules of Civil Procedure.

In Illinois, the discovery process in civil litigation is governed by the Illinois Code of Civil Procedure. This process allows parties to obtain evidence from each other to prepare for trial. It includes the exchange of documents and tangible items through requests for production, answering written questions under oath known as interrogatories, and taking oral depositions of witnesses. Illinois law also requires certain disclosures to be made automatically without a formal request from the opposing party. Additionally, parties may issue subpoenas to third parties for the production of documents or to provide testimony. The scope and limits of discovery, the time frames for responding to discovery requests, and the assertion of privileges to protect certain information from being disclosed are all dictated by the state's procedural rules. Discovery can be a complex and costly aspect of litigation, but it is crucial for the parties to gather the necessary evidence to support their cases. The Illinois Supreme Court Rules, particularly Rules 201 through 219, outline the specific procedures and requirements for conducting discovery in the state.