Before 1970, no generally accepted foundation existed for comprehensive rules for criminal discovery. Both the 1970 and 1978 standards set forth general purposes for discovery. The overall goal of affording discovery in criminal cases is to permit thorough preparation for trial and to minimize surprise at trial. Discovery also assures equality in pretrial disclosure to all similarly situated defendants. The standards are applicable in all serious criminal cases. They do not explicitly describe which stage in the criminal proceeding triggers the beginning of discovery. Under these standards, the prosecutor must disclose all evidence favorable to the accused and the names of all witnesses. Similarly, relevant recorded statements must be disclosed by the prosecutor, including the statements of experts. Records of prior convictions must also be revealed. The standards additionally require disclosure of matters affecting the admissibility of evidence at trial. The concept of reciprocity in discovery with regard to defense information is advanced by the standards. These standards are now used by many States as a model. How well discovery works in any given jurisdiction, however, depends upon more than the mere adoption of rules. It also depends upon the way the trial court exercises its considerable discretion in enforcing the rules. Generally, under these standards the prosecutor benefits most from the grand jury investigation. For the defense, the most important discovery device is likely to be the preliminary hearing. The Supreme Court of Illinois recently authorized the use of the preliminary hearing for yet another purpose. In 'People ex rel. Fisher v. Carey' (1979), the court stated that discovery rules in Illinois apply only after preliminary hearing but also acknowledged that the power to subpoena is not determined by discovery rules. The rules are indispensable to any criminal proceeding. The article includes 369 footnotes.