The lightsaber is a fictional weapon that plays a key role in the movies, games and novels that constitute the Star Wars universe. Lightsabers are science fiction versions of their namesake, the saber, which instead of a metal blade holds an energy blade with a length of about one meter long. Lightsabers differ in color based upon the specific crystal used in construction. Though they often behave like regular swords, they have been depicted as able to penetrate and cut through most matter with little or no resistance (due to their energy-based nature), and to deflect energy, such as shots from blasters (the ranged weapons used in the Star Wars franchise), Force Lightning thrown by Sith Lords, and other lightsabers.

The lightsaber first appeared in the film Star Wars Episode IV: A New Hope (1977). At first, the effect was created by a handle with a motorized spinning reflector and pointing high-intensity light in their direction. The outcome was not satisfying, so in post-production the effect was augmented through rotoscoping. For Episodes V and VI the use of reflective tape was abandoned and the effect was achieved by rotoscoping rods made of aluminum and later carbon fiber rods. For the prequel trilogy, the effect was created using computer animation.

Within the fiction of Star Wars, the lightsaber "blade" is made by a very tight loop of highly focused energy, possibly a loop of plasma contained in a strong magnetic or other field which compresses the circular loop so much that it looks like a cylindrical bar. When deactivated, a lightsaber appears as a polished metallic handle, about 30 centimeters long, with or without an ignition button. They are carried at the waist in this fashion by belt clip, and can be drawn by hand or by the Force (as was done by master Yoda in Episode II: Attack of the Clones). Lightsabers have a distinctive hum when active. Some carry a "dead-man trigger" that deactivates the saber automatically if dropped.

To carry a lightsaber is a reflection of confidence, dexterity, and attunement to the Force. Although use of the lightsaber is not strictly reserved to Jedi (see General Grievous), the only others widely known of being capable of handling the difficult weapon are the Sith: Darth Maul, Darth Tyranus (Count Dooku), Darth Vader and Darth Sidious (Palpatine), as well as other Sith characters in the Expanded Universe. According to a 2008 survey of approximately two thousand film fans, conducted by 20th Century Fox, the lightsaber is the most popular film weapon.