Combat engineer, also called pioneer or sapper in many armies, is a soldier who performs a variety of construction and demolition tasks under combat conditions. Such tasks typically include constructing and breaching trenches, tank traps and other fortifications, bunker construction, bridge and road construction or destruction, laying or clearing land mines, and other physical work in the battlefield. More generally, the combat engineer's goals involve facilitating movement and support of friendly forces while impeding that of the enemy.

Usually, a combat engineer is also trained as an infantryman, and combat engineering units often have a secondary role fighting as infantry. Beyond self-defense, combat engineers, infantry and assault troopers from armored corps units are generally the only troops that engage in the assault while dismounted