Abstract: The Supreme Court's decision in Lawrence v. Texas is best seen as a cousin to Griswold v. Connecticut, invalidating a ban on the use of contraception within marriage, and Reed v. Reed, invalidating a preference for men over women in the administration of estates. In both cases, the Court struck down an anachronistic law palpably out of step with existing public convictions. Lawrence should be understood in the same terms, as rooted in a distinctly American-style doctrine of desuetude. The central principle is that at least if certain interests are involved, criminal statutes may not be invoked against citizens when the underlying moral judgments have become anachronistic, as demonstrated by a pattern of nonenforcement. A key problem here is procedural; it involves an absence of fair notice and arbitrary exercise of discretion. This understanding of the decision has implications for the many imaginable constitutional challenges to other laws involving sex and sexual orientation. After Lawrence, states are certainly prohibited from banning fornication; they are almost certainly forbidden to ban use of sexual devices. Bans on prostitution, incest, and adultery stand on firmer grounds, though even here responsible challenges can be imagined. After Lawrence, the Constitution almost certainly forbids public discrimination against those who have engaged in homosexual conduct, at least outside of certain specialized contexts (most notably the military). The hardest cases involve the failure to recognize same-sex marriages. The ban on same-sex marriages cannot be said to be an anachronism, even though it is not easy, in principle, to reject the law struck down in Lawrence while permitting states to deny gays and lesbians the right to marry. One general lesson, underlined by Lawrence, is that political and social change is usually a precondition for changed interpretation of the Constitution.