In Call of Duty: Black Ops, Contracts are designed to assist the player in leveling up as they offer potential rewards of CODPoints and experience Points (on some) for completing certain challenges within a provided time limit.
Contracts also reappear in Call of Duty: Black Ops III. They were added in the May 6th update.
Contracts are available for purchase from the multiplayer menu with CODPoints. Different contracts have different goals, such as achieving a certain number of killstreak rewards, or earning a certain amount of kills with a specific weapon. Contracts will reward players upon completion with CODPoints, Experience points, or a combination of the two. The higher in difficulty the contract has the bigger output of CODPoints or Experience points the player will receive upon completion.
Once players accept any contract, they have a certain amount of time to fulfill it. This is generally either forty minutes or an hour, depending on the difficulty and type of the contract. The timer only counts down when the player is in an active part of the game. Time spent dead waiting to respawn in games with delayed spawns, such as Search and Destroy or Capture the Flag does not run down this time limit. Also, contracts only applicable to one mode will not expire while playing a different mode. For example, players will not lose time on a Team Deathmatch Contract if they are playing a game of Domination. Contracts are not carried across playlists, either, so a Team Deathmatch contract will not expire if the player plays a Team Deathmatch game on the Barebones or Hardcore playlists.
There are three different categories of Contracts:
Mercenary contracts involve achieving kills and killstreaks in general or kills with a specific gun.
Operations contracts involve match related objectives (such as "Win two games of Capture the Flag").
Specialist contracts are mostly specific to certain weapons or Perks (i.e. Five headshots with the AUG).
Players can have no more than three Contracts, one from each category, active at any time. Selecting a new Contract removes an existing Contract of the respective category; should the contract be incomplete, the player's CODPoints are not refunded. The available set of Contracts changes each day, and completed or expired contracts reset hourly. This means that a player can complete the same contract multiple times within a day before that set of contracts change. Purchased Contracts can still be completed after this daily update as long as the time spent alive in-game has not run out. It is important to note that there are no contracts for classified weapons. However, the player can still use them to complete contracts that involves their weapon type.
Also, the player cannot buy a weapon-specific contract if the weapon is not unlocked, but the player can if the weapon is unlocked but not bought.