Call of Duty 4: Modern Warfare is a first-person shooter similar to previous games in the Call of Duty series, but set in the present-day instead of World War II.
The game's move to modern warfare introduces new weapons and technology to the Call of Duty franchise, including the M203 grenade launcher, M4A1 carbine, the AN/PEQ-2 Target Pointer for use in conjunction with night vision goggles, the MP5SD submachine gun, and the FGM-148 Javelin portable anti-tank guided missile. The player gains access to these over the course of the game, but may only carry up to two weapons in addition to grenades. Weapons from fallen foes can be picked up to replace weapons in a player's arsenal. Players also have additional abilities, including a grenade launcher attachment, night-vision goggles, and the ability to call in airstrikes.
The gameplay of Call of Duty 4 shares several features with previous iterations of the franchise. Once again, players fight alongside AI-controlled teammates. They help during the game's missions by providing cover fire, shooting down enemies, and clearing rooms for entry.
A character can be positioned in one of three stances: standing, kneeling, or prone; each affecting the character's rate of movement, accuracy, and stealth. Using cover helps the player avoid enemy fire or recover health after taking significant damage, as there are no armor or health powerups. When the character has taken damage, the edges of the screen glow red and the character's heartbeat increases. If the character stays out of fire, the character can recover. When the character is within the blast radius of a live grenade, a marker indicates the direction of the grenade, helping the player to either flee or toss it back to the enemy.