The sling was likely mankind's first, true projectile weapon. It generally consists of two cords and a pouch. These cords are held in one hand and a projectile is placed in the pouch. The length of the sling provides greater mechanical advantage than one's arms. Projectiles can be slung over 1500 feet (450m) at speeds exceeding 250 miles per hour (400 kph). The sling is unique in that the movement of the weapon is merely an extension of the user’s body. The power and accuracy of the weapon is not by technological means, but rather user skill. The connection between slinger and sling is an intimate one, a relationship rarely found in modern weaponry.
Slinging.org has the history of the sling, information on different kinds of slings, and advice on making and using a sling. Link -via Everlasting Blort