A Practice Note outlining the course of antitrust investigations conducted by the Department of Justice (DOJ) and the Federal Trade Commission (FTC) before they start enforcement proceedings. This Practice Note discusses how the antitrust agencies commence an investigation, whether civil or criminal, the use of civil investigative demands (CIDs) to compel production of evidence, as well as their issuance and service, and compliance with CIDs. It also discusses the use of search warrants, wire taps, interviews, and grand jury subpoenas, whether duces tecum or ad testificandum in criminal investigations, as well as the Fifth Amendment privilege against self-incrimination.