Rule 501 states, 'Except as otherwise required by the Constitution of the United States or provided by Act of Congress or in rules prescribed by the Supreme Court pursuant to statutory authority, the privilege of a witness, person, government, State, or political subdivision thereof shall be governed by the principles of the common law as they may be interpreted by the courts of the United States in the light of reason and experience.' Prior to the passage of the Federal Rules, the Federal courts began the development of a body of law to govern the law of spousal privilege. The Supreme Court's decision in Hawkins v. United States (1958) held that a defendant had the right to bar his/her spouse from providing adverse testimony, even should the spouse volunteer to offer such testimony. The Court did, however, make the reservation that the decision 'does not foreclose whatever changes in the rule may eventually be dictated by 'reason and experience.'' 'Until 1980, the practical effect of rule 501 was to contine the Hawkins rule. On February 27, 1980, however, in Trammel v. United States, the Supreme Court abolished the feature of the Hawkins rule that permitted a defendant marital partner to prevent adverse spousal testimony unilaterally. The Court modified the rule so that the witness spouse alone has the privilege to refuse to testify adversely. Implications flowing from this decision are discussed. A total of 299 notes are listed.