Boone Carlyle is a fictional character played by Ian Somerhalder on the ABC drama television series Lost, which chronicles the lives of the survivors of a plane crash in the south Pacific. Boone is introduced in the pilot episode as the stepbrother of fellow crash survivor Shannon Rutherford. He tries to contribute as much as he can to the safety of the castaways and eventually becomes John Locke's protégé.

Unlike many other characters of the first season, who were rewritten based on their actors, Boone was largely the same through production. Somerhalder did not want to shoot a pilot; however, he jumped at the opportunity once he found out he would be working with co-creator/executive producer J. J. Abrams. The character was generally well received by critics and fans; USA Today described Boone as a "callow, privileged young man striving for maturity."

Boone is born in October 1981, the son of wealthy Sabrina Carlyle, the head of a wedding company. When Boone is ten years old, Sabrina marries Adam Rutherford, who has an eight-year-old daughter named Shannon. When Boone is twenty years old, he becomes the chief operating officer of his mother's business in New York City. Boone harbors a fondness for his stepsister, which develops into a romantic attraction. When Boone learns of Shannon's financial difficulties after her father's death, he offers to give her money, but she does not accept. Boone "rescues" Shannon several times from abusive relationships by paying the boyfriends to leave her. One such rescue attempt leads Boone to Sydney, Australia in September 2004, where he learns the relationships are actually scams concocted by Shannon to get his money and attention. Boone is deeply hurt by the deception. Boone and Shannon have sex after her Australian boyfriend runs away with her money. The next day, they board Oceanic Airlines Flight 815 to return to the United States.

Boone unsuccessfully tries to perform CPR on an unconscious Rose Henderson, which he claims to have learned when he was a lifeguard. Boone maintains a generally helpful attitude and remains protective of Shannon (his sister), although he criticizes her for her affectedness. His protective attitude combines with jealousy when she develops feelings for Sayid Jarrah, and Boone unsuccessfully attempts to discourage the relationship.

Boone is drawn to the hunting and survival skills of John Locke, a fellow castaway. He becomes Locke's apprentice and begins to distance himself from the other survivors. Boone and Locke find a metal hatch while tracking the kidnapped Claire Littleton and Charlie Pace. The two excavate the hatch, keeping its existence a secret from the other survivors. Locke subjects Boone to a hallucinatory exercise on their twenty-fourth day on the island, allowing Boone to resolve his feelings for Shannon, in which Boone sees Shannon after she is killed by the monster. Forty-one days after the crash, Boone and Locke discover a heroin runner's Beechcraft plane stuck high in a tree canopy. Boone climbs up into the aircraft and finds a working radio in the cockpit, which he uses to transmit a mayday signal. He receives a response to his message from a man, later revealed to be Bernard Nadler of the tail-section survivors, but the aircraft unbalances and falls nose-first to the ground. Boone sustains severe injuries and, despite Jack's attempts to treat him, dies on November 2, 2004. Boone tries to pass a message to Shannon through Jack, but dies before he is able to finish the sentence. Somerhalder said the news of his character's death—the first death of a major character on the series—was "pretty devastating."

Almost four weeks later, Locke experiences a self-induced hallucination, in which a longer-haired Boone appears and pushes Locke around in a wheelchair in an imaginary Sydney International Airport, with the other survivors present but acting in different roles. Boone tells Locke someone in the airport is in serious danger. Close to the end of the hallucination, Locke finds Eko's stick covered in blood and Boone appears bloody and injured. He tells Locke, "They've got him. You don't have much time." In the Oceanic Six's cover story, Boone survived the initial crash but soon died of internal injuries.

In the alternate timeline, Shannon does not go back with Boone. In "LA X", Boone goes back alone on Flight 815 and sits beside Locke, who tells him about going on a walkabout in Australia. In a parallel with the island timeline, Boone tells Locke that if they crashed, he would follow him. Once the plane lands, Boone shakes Locke's hand and exits the plane. Boone reappears in the final episode of Lost. In "The End", we see Hurley and Sayid talking in a car on a dark street, then witnessing a thug beating up Boone outside a bar. Shannon shouts, "Leave my brother alone," and Sayid gets out of the car to intervene. His and Shannon's memories are restored the moment they touch. Boone, having conspired with Hurley to bring Shannon and Sayid together, wanders over to the car. He jokes with Hurley about how he had to take a beating and adds sarcastically, "Thanks for taking your time." He also comments how difficult it was to get Shannon to return from Australia with him, but he and Hurley agree the effort was worth it to have her and Sayid's memories restored. Boone is one of the first people Jack greets in the church where everyone reunites to move on to the afterlife together.

USA Today described Boone as "a callow young man who had been toughened by island challenges." Variety called him "hot-headed", while Entertainment Weekly wrote he was "even-tempered". Boone's quick decisions with good intentions are often rash. On his sixth day on the island, Joanna Miller drowns. As soon as he finds out she is drowning, he immediately tries to save her, although he does not succeed and almost becomes a casualty himself. While trying to take on a leadership role, Boone steals the camp's water; however, his plan backfires and the survivors turn on him. When Boone suspects Sawyer has Shannon's medicine, he attempts to steal it. Aside from Shannon, he is closest to John Locke, who acts as a father figure and mentor to the younger, inexperienced Boone and who, unlike others including Shannon, tries to help him do his part on the island. Boone similarly is one of the few to trust Locke's guidance and make Locke feel like the hero he has always wanted to be. Boone reflects aspects of Locke's personality, such as his desire to have a unique purpose and his willingness to believe in the unlikely.