Challenge

Challenges in the Call of Duty series can be linked to Achievements or Trophies. The player will gain XP for performing an action or series of actions in a multiplayer match. Some challenges are linear, like the Marksman challenges, which are awarded for getting a specific number of kills for a given weapon. Some are more imaginative. "How the ?" is a perfect example, being gained by killing an enemy by setting off an explosive by shooting it through a wall. Attempting to complete challenges, particularly the more difficult ones can serve as an incentive to players who might otherwise grow bored with a game, though with enough variation and playing time, almost every challenge can be completed unintentionally.

In Call of Duty 4: Modern Warfare, challenges are awarded to the player in 5 Tiers and increase experience points depending on the difficulty the challenge was to complete. Each one is more challenging than the previous. While the normal challenges give out 50-250 experience points, the weapon-based challenges can give up to 1000 XP when they are completed. Marksman challenges are based on the amount of kills with a weapon, and unlock special attachments like a Silencer or Red Dot Sight to attach to the weapon the challenge was achieved with. Weapon Expert challenges unlock "weapon camouflages" (alternate skins for a weapon) in a similar fashion, though only headshots are counted.

In Call of Duty: World at War, challenges are given to the player in seven tiers. Each one is also more challenging than the previous.

Boot Camp challenges (or Basic Training in MW2) are seen as the least difficult with even the most mediocre players completing them by either Rank 55 in Call of Duty 4: Modern Warfare, Rank 65 in Call of Duty: World at War or Rank 70 in Call of Duty: Modern Warfare 2.

In Call of Duty: Modern Warfare 2, Challenges unlock new Titles, and Emblems, as well as giving the player experience points. The highest amount of experience that can be gained for any one challenge is 10,000. List of Challenges in Modern Warfare 2: Primary Weapons, Secondary Weapons, Perks, Equipment, Basic Training, Operations, Killstreak, Precision, Finishing Moves, Humiliation, Payback, Elite, Intimidation, Prestige.

In Call of Duty: Black Ops, challenges no longer allow the player to unlock weapons, attachments, camouflages, titles, facepaint, emblem layers etc. These are unlocked by reaching a certain rank and purchasing the item. Challenges are still present in the game; however their only purpose is to a) reach the Pro version of perks and b) gain raw XP to help rank up.

List of Weapon Challenges

 * Marksman Challenges - get a certain amount of kills with the weapon
 * Expert Challenges - get a certain amount of headshot kills.
 * Veteran Challenges- get a certain amount of kills with a weapon after prestige. (only in Call of Duty: Modern Warfare 2)
 * Master Challenges- get a certain amount of headshots after prestige. (only in Call of Duty: Modern Warfare 2)
 * Mastery Challenge- unlock all attachments for a weapon.

List of Challenge Tiers

 * Boot Camp
 * Operations
 * Vehicle
 * Field Specialist
 * Killer
 * Humiliation
 * Elite
 * Perks
 * Equipment
 * Basic Training
 * Killstreak
 * Precision
 * Finishing Moves
 * Payback
 * Intimidation
 * Prestige

Call of Duty: World at War challenges
Challenges are back and use the same system as Call of Duty 4. When a challenge is complete, the player will receive XP, and weapon Marksman challenges award the player with weapon attachments as well. Challenges are unlocked at Level 5.

Marksman challenges may award the player with attachments like the Aperture Sight, Telescopic Sight, Rifle Grenade, Extra Munitions, Sniper Scope or Bayonet. Certain weapons allow certain attachments.

Call of Duty: Modern Warfare 2 Challenges

 * See Call of Duty: Modern Warfare 2 Challenges

Call Of Duty: Black Ops Challenges

 * See Call of Duty: Black Ops Challenges