Grand Theft Auto IV and its downloadable episodes The Lost and Damned and The Ballad of Gay Tony, introduces a new cover system (one that is not so different from the one used in the Gears of War series.)
By pressing a button, the Protagonist will hide behind the nearest available cover, with a great number of animations for each way he enters cover (such as crouching behind a car, rolling to reach a cover faster, and even sliding on his knees). Behind cover, the player can lock-on enemies (or manually aiming to them) exposing himself when the fire button is pressed, and retreating back when he ceases fire. The protagonist can also blind fire,but the accuracy is significantly decreased and the player is unable to lock-on to enemies.
In Multiplayer using cover can save your life in many occasions.