The federal grand jury exists to investigate crimes against the United States and to secure the constitutional right of grand jury indictment. Its responsibilities require broad powers. As an arm of the U.S. District Court which summons it, upon whose process it relies, and which will receive any indictments it returns, the grand jury's subject matter and geographical jurisdiction is that of the court to which it is attached. This book provides a brief general description of the federal grand jury, with particular emphasis on its more controversial aspects -- relationship of the prosecutor and the grand jury, the rights of grand jury witnesses, grand jury secrecy, and rights of targets of a grand jury investigation. The book also provides an overview of the law under the federal material witness statute which authorises the arrest of material witnesses, permits their release under essentially the same bail laws that apply to federal criminal defendants, but favors their release after their depositions have taken.