The recognized purpose of discovery under the Federal Rules of Civil and Criminal Procedure is to formulate issues and to ascertain facts and information relative to those issues before trial by forcing a full disclosure. The trial of antitrust cases is so complex that the judiciary has found it necessary to rely on uniform guidelines. Nevertheless, most important trial decisions affecting the future direction of antitrust law are made in the context of discovery controversies. Permissible methods of pretrial discovery under the Federal rules are depositions, interrogatories, requests for the production of documents and other tangibles or for permission to inspect documents, and requests for admissions. The criterion for discovery is whether the information sought is relevant to the subject matter of the action. Relevancy is not governed by rules of evidence and is not limited to matters raised by the pleadings. Depositions, the most frequently used method of discovery, are used both for discovery and to perpetuate testimony. There are additional methods of discovery peculiarly available to the Government which provide it with advantages virtually unsurpassed by private parties. These methods include the investigative grand jury, civil investigative demands, and agency investigations by the Federal Trade Commission and the Antitrust Division of the Department of Justice. Access provided private parties to information held by the Government varies from case to case. Information is most often obtained under authority of the Freedom of Information Act; additional sources of information include prior judgments and decrees. Third-party information is frequently necessary in preparing an antitrust case for trial. Both formal and informal requests are made of third parties. The primary limitation on pretrial discovery is that imposed by the Federal rules of procedure such as the requirement of relevance to the subject matter of the action. However, discovery is frequently and successfully resisted, even where the requisite relevancy is present. Liberal discovery is curtailed under historical doctrines of privilege, matters of policy, and exemptions specified under the Freedom of Information Act. All of these limitations have been judicially recognized; nevertheless, courts impose these limitations in varying degrees. The article includes 130 footnotes.