In the federal court, civil trials are conducted according the Federal Rules of Civil Procedure, and criminal trials must abide by the Federal Rules of Criminal Procedure. There are also rules governing the presentation of evidence. The states have either adopted the federal rules, with their own modifications, or have developed their own rules for civil and criminal procedure. These rules do not apply to agency proceedings. Instead, federal agencies are governed by the Administrative Procedure Act (APA), and each state has a comparable set of rules for its agencies. The APA sets out how administrative hearings are conducted, and how the agencies make regulations.

These hearings are presided over by an administrative law judge (ALJ). These are generally much more informal than trials. Agencies usually allow regulated parties to talk directly to the staff, who may help the regulated party prepare its case or comply with the regulation. Unlike a judge in an adversary civil or criminal case, the ALJ is often an expert in the area, either because of special training or through years of reviewing cases on the same issues. Agency hearings do not have juries. Although live witness testimony is permitted, agencies generally prefer written reports from experts because they are easier to evaluate than live testimony.