'Lascannon' is a term from Warhammer 40,000 used to refer to pulsed lasers with a long cycle time, and a size near the limits of man-portability. A laser of this size is easily capable of bringing down a regular-sized tank, and a glancing hit will kill even heavily-armoured personnel. Similarly sized laser weapons with rapid fire rates are known as Multilasers, the increased fire rate typically coming at the expense of damage and armour penetration. The multilaser is most commonly seen on the Chimera APC and Sentinel walker of the Imperial Guard.

Laser weapons in general are often used by non-elite troops as they are cheap to manufacture, easily mass-produced, and require little maintainance. The only ammunition required is an energy source, and there are few (if any) moving parts to break or jam. While Orks do use lascannons, they consider them not very 'shooty', prefering weapons that make loud noises and big explosions to weapons that cut and melt.

The Imperium's laser weapons all take the same standardised power pack, which is sealed against the elements, and can be recharged from most vehicles, by leaving it in the sun, or in emergencies by burning a campfire on top of it. While laser pistols and rifles can fire many shots from one power pack, the lascannon fires only one, and may accept many power packs at once.

Lascannons are large - more than six feet long, and very heavy. While orks and space marines can comfortably aim and fire a lascannon carried on the shoulder, the non-enhanced humans of the Imperial Guard typically mount theirs on a carriage or tripod, operated by two-man 'weapons teams' - one guardsman operating the weapon, the other taking care of loading and maintaining it. The Tarantula point defense weapon mounts two lascannons on a self-propelled carriage, with computer-controlled firing.

Lascannons are the primary armament on many of the Imperium's tanks, including the Leman Russ, Predator and Land Raider, and a secondary weapon to deter regular tanks from attacking super-heavy vehicles such as the Shadow Sword and Leviathan.