A lightsaber (or lightsabre, see spelling differences) is a fictional weapon in the Star Wars universe, a "laser sword." It consists of a polished metal hilt which projects a blade of plasma about 1.33 meters long. The Lightsaber is the signature weapon of the Jedi order and their Sith counterparts, both of whom can use them for close combat, or to deflect blaster bolts. Its distinct appearance was created using rotoscoping for the original Star Wars films, and digitally for the prequel trilogy. The Lightsaber first appeared in the original Star Wars film (1977) and every Star Wars movie to date (except The Star Wars Holiday Special) has featured at least one Lightsaber duel. In 2008, a survey of approximately 2,000 film fans found it to be the most popular weapon in film history.

The Lightsaber's blade cuts through most substances without resistance. It leaves cauterized wounds in flesh, but can be deflected by another Lightsaber's blade, or by energy shields. Some exotic saber-proof materials have been introduced in the Expanded Universe. An active Lightsaber gives off a distinctive hum, which rises in pitch and volume as the blade is moved rapidly through the air. Bringing the blade into contact with an object or another Lightsaber's blade produces a loud crackle.

The term "Lightsaber" has been applied to other similar weapons in science fiction.