Cite as: 582 U. S. ____ (2017) 1 Opinion of the Court NOTICE: This opinion is subject to formal revision before publication in the preliminary print of the United States Reports. Readers are requested to notify the Reporter of Decisions, Supreme Court of the United States, Wash­ ington, D. C. 20543, of any typographical or other formal errors, in order that corrections may be made before the preliminary print goes to press. SUPREME COURT OF THE UNITED STATES _________________ No. 15–1191 _________________ JEFFERSON B. SESSIONS, III, ATTORNEY GENERAL, PETITIONER v. LUIS RAMON MORALES-SANTANA ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE SECOND CIRCUIT [June 12, 2017] JUSTICE GINSBURG delivered the opinion of the Court. This case concerns a gender-based differential in the law governing acquisition of U. S. citizenship by a child born abroad, when one parent is a U. S. citizen, the other, a citizen of another nation. The main rule appears in 8 U. S. C. §1401(a)(7) (1958 ed.), now §1401(g) (2012 ed.). Applicable to married couples, §1401(a)(7) requires a period of physical presence in the United States for the U. S.-citizen parent. The requirement, as initially pre­ scribed, was ten years’ physical presence prior to the child’s birth, §601(g) (1940 ed.); currently, the requirement is five years prebirth, §1401(g) (2012 ed.). That main rule is rendered applicable to unwed U. S.-citizen fathers by §1409(a). Congress ordered an exception, however, for unwed U. S.-citizen mothers. Contained in §1409(c), the exception allows an unwed mother to transmit her citizen­ ship to a child born abroad if she has lived in the United States for just one year prior to the child’s birth. The respondent in this case, Luis Ramón MoralesSantana, was born in the Dominican Republic when his father was just 20 days short of meeting §1401(a)(7)’s