View source for Sneak Attack

You know how to strike subtly and exploit a foe's distraction. Once per turn, you can deal an extra 5d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

You don't need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn't incapacitated, and you don't have disadvantage on the attack roll.