Skirmishers are soldiers who make up a Skirmish Line. A Skirmish line is mainly used to protect flanks, or to harass the enemy line. Skirmishers are generally lightly armed and lightly armored in order to move quickly from one side of the field to the other.

In medeival warfare, skirmishers were lightly armed troops, typically carrying javelins, slings and leather shields. Due to their light arms and armour, they could run ahead of the main battle line, fire a volley of slingshots or javelins, and retreat back behind the main battle lines before the battle lines closed for the battle. The main aim of skirmishing was to entice unruly armies into a rash attack. Skirmishing could also be effectively used to hem in tight groups of infantry with very less shielding. Flanking maneuvres carried out by skirmishers in the absence of cavalry were very effective.

Once the skirmishing was done, the warriors could either stay in the relative safety behind friendly infantry shooting into thick enemy formations, or could participate in an auxiliary role, either in melee combat as light infantry (with daggers or short swords) or logistically, for artillery ammunition, or as surgeons and medics in the battlefield.

During the American Civil War it was common for Cavalry to dismount and take a Skirmish line in order to accomplish the same mission of their Roman and Medieval counterparts.

Due to their lightness, skirmishers were also valuable for reconnaissance and as scouts, especially in wooded areas. Later, after gunpowder, a thin skirmisher line could be used to find out the spread of enemy front lines from the sound of gun fire. This was used effectively by General Lee in the initial stages of the American Civil War.

During the Napoleonic wars, Skirmishers played a key role in battles, by punching holes in the enemy ranks. The Infantry of the time would fire volleys almost without aiming so a loose screen of skirmishers was a hard target. French Voltigeurs and British Rifles where some of the best units during the Napoleonic wars.