O n June 27, 2018, Justice Anthony M. Kennedy announced that, effective July 31, 2018, he would retire from active service as an Associate Justice on the Supreme Court of the United States. Nominated to replace Justice Lewis Powell in 1987, Justice Kennedy has been one of the longest-serving Justices in the history of the Court. His decisive role on the Court, particularly during the Roberts Court era, cannot be overstated. While Justice Kennedy has been a critical vote on the Court for much of his 30-year tenure, since the October 2005 term that marked the beginning of the Roberts Court, Justice Kennedy has been the Court's "median Justice," voting for the winning side in a case more often than any of his colleagues in 9 out of 12 terms. During this era, the High Court issued a number of landmark rulings that spanned the ideological spectrum. For instance, during the Roberts Court era, the Court held that the Fourteenth Amendment to the Constitution requires states to recognize marriages between same-sex couples in the same circumstances as they recognize marriages between opposite-sex couples; invalidated state laws viewed to impose an "undue burden" on a woman's right to terminate a pregnancy; afforded enemy belligerents detained at Guantanamo Bay certain procedural protections; and concluded that the Eighth Amendment prohibits the states from imposing the death penalty or a sentence of life without parole in certain circumstances. At the same time, since 2005, the Court also struck down campaign finance laws banning corporate independent expenditures for electioneering communications; invalidated Section 5 of the Voting Rights Act of 1965 on federalism grounds; recognized that the Second Amendment protects an individual's right to possess a firearm and to use that firearm for lawful purposes; upheld President Trump's proclamation placing entry restrictions on foreign nationals from specified countries; and invalidated on First Amendment grounds state laws that aimed to regulate certain commercial activities. In all of these cases, the sitting Justices were closely divided, and the composition of Justices in the deciding majority in such cases shifted dramatically from case-to-case with one exception: Justice Kennedy. Perhaps because of his pivotal role on the Court, like Justice Powell whom he succeeded, Justice Kennedy was viewed by many to be the Court's "swing" vote. The label of being a "swing vote" on the Court, however, may invite misleading conclusions about Justice Kennedy's approach to cases. As several commentators have noted, Justice Kennedy's jurisprudence did not necessarily focus on compromise or balance in the Court's decisions, but was instead, at times, informed by principles that resulted in votes that could not be categorized uniformly by a conservative or liberal ideology. For his part, Justice Kennedy resisted the "swing vote" moniker, declaring in a 2015 interview that "[t]he cases swing, I don't." As a result, an examination of the underlying cases in which Justice Kennedy cast critical votes during the Roberts Court era may be necessary to fully gauge his jurisprudence and the significance of his retirement. This report provides a broad overview of Justice Kennedy's approach to the law, with a particular emphasis on how he interpreted the Constitution. The report then discusses what his retirement may mean for the future of the Court in various areas of the law, broadly noting key legal decisions during the Roberts Court era in which Justice Kennedy cast a decisive vote. The report does not, however, purport to discuss fully every area of law that Justice Kennedy considered during his more than three decades of service on the Court. Nonetheless, guided by several tables in the Appendix noting the opinions in which Justice Kennedy cast decisive votes during the Roberts Court era, the report highlights key aspects of Justice Kennedy's jurisprudence and the key legal issues where his absence from the Court could result in a shift in the Court's jurisprudence. On July 9, 2018, President Trump announced the nomination of Judge Brett M. Kavanaugh of the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) to fill the impending vacancy on the Supreme Court caused by Justice Kennedy's scheduled retirement. CRS reports analyzing Judge Kavanaugh's jurisprudence on particular areas of the law, as well as a tabular listing of lower-court decisions in which he authored opinions, are in preparation. As one legal scholar has observed, "identifying Justice Kennedy's judicial philosophy is no easy task." Unlike Justice Antonin Scalia, his colleague for nearly 28 years on the High Court, Justice Kennedy did not subscribe to a particular judicial philosophy, such as originalism or textualism. In his 1987 confirmation hearings, Justice Kennedy eschewed committing himself to a "single, overarching theory" of legal interpretation. For instance, in response to a question posed by Senator Robert Byrd concerning the role of history when interpreting the Constitution, the nominee opined that a judge cannot rely only on "history in order to make the meaning of the Constitution more clear," and that "new generations" can also "yield new insights and new perspectives" that change "our understandings" of the Constitution. These and similar statements made during his confirmation hearing appear to have presaged the approach taken by Justice Kennedy on the Court, wherein he often synthesized several approaches to judging to guide his decision as to the appropriate result in a given case. Justice Kennedy's approach to judging appeared informed by certain guiding principles, three of the most determinative of which are discussed below. Justice Kennedy's jurisprudence was often grounded in concerns for personal liberty, that is, freedom from government interference with "thought, belief, expression, and certain intimate conduct." The Justice's concerns for liberty manifested themselves in several free speech cases, wherein Justice Kennedy took the view that the First Amendment prohibited government actions that told individuals what they could say or what they could hear. For instance, on the day before he announced his retirement, Justice Kennedy authored a concurring opinion to explain how government paternalism with respect to speech could "imperil[]" liberty: It is forward thinking to begin by reading the First Amendment as ratified in 1791; to understand the history of authoritarian government as the Founders then knew it; to confirm that history since then shows how relentless authoritarian regimes are in their attempts to stifle free speech; and to carry those lessons onward as we seek to preserve and teach the necessity of freedom of speech for the generations to come. . . . Freedom of speech secures freedom of thought and belief. In this vein, Justice Kennedy, on behalf of the Court in Citizens United v. FEC, struck down a federal campaign finance law banning corporate independent expenditures for electioneering communications, rejecting arguments that the government needed to police corporate political speech. For Justice Kennedy, when the "[g]overnment seeks to use its full power . . . to command where a person may get his or her information or what distrusted source he or she may not hear, it uses censorship to control thought" in violation of the First Amendment. This rationale undergirded several other cases in which Justice Kennedy viewed the First Amendment to impose clear limits on the government's ability to regulate speech within the commercial sphere. Justice Kennedy's emphasis on liberty also manifested itself in a number of decisions he authored or joined on issues implicating religion. For instance, in Church of Lukumi Babalu Aye v. City of Hialeah , Justice Kennedy, on behalf of the Court, struck down a set of ordinances enacted by a Florida city prohibiting animal sacrifice, viewing the challenged laws as designed to "persecute or oppress" adherents to the Santeria religion. In so doing, Justice Kennedy cautioned against "state intervention stem[ming] from animosity to religion or distrust of its practices," and identified what he viewed to be the "high duty" imposed on government officials by the First Amendment: to "commit[] government to religious tolerance." Quoting Lukumi 25 years later in his opinion for the Court in Masterpiece Cakeshop v. Colorado Civil Rights Commission, Justice Kennedy concluded that a state civil rights commission violated its "duty" to not treat a party before it with hostility because of that party's religious beliefs. Likewise, expressing concern over the "danger[s] to liberty" that "lie" when the state excludes religious groups from a public forum or exhibits viewpoints based on hostility toward religion, Justice Kennedy wrote or joined several opinions that resulted in public spaces being opened for use by religious entities. Nonetheless, the soon-to-be-retired Justice viewed the constitutional requirement of tolerance to apply to how religious adherents treated the nonreligious, as well. Writing for the Court in Lee v. Weisman, Justice Kennedy held that the First Amendment's Establishment Clause prohibited a sectarian invocation and benediction at a public school graduation ceremony, maintaining that "prayer exercises in public schools carry a particular risk of indirect coercion" for objecting students, who may feel embarrassed or pressured by the state's action. Beyond the realm of the First Amendment, Justice Kennedy's liberty jurisprudence animated a number of decisions in which the Court struck down several federal and state laws on either equal protection or substantive due process grounds. In particular, his substantive due process cases seemed informed by a particular consideration related to liberty—the belief that the government must treat individuals with "dignity" —when concluding that a government measure either infringed upon an individual's right to privacy or involved the sanctioned animus toward a particular group. For instance, in Planned Parenthood of Southeastern Pennsylvania v. Casey, a plurality opinion of the Court authored by Justice Kennedy, along with Justice Sandra Day O'Connor and Justice David Souter, declared that the Constitution prohibits the government from interfering with certain life decisions "central to personal dignity and autonomy" because at the "heart of liberty" "is the right to define one's own concept of existence, of meaning, of the universe, and of the mystery of human life." For the Casey plurality, "there is a realm of personal liberty which the government may not enter."