Assassination contracts are side missions in Assassin's Creed IV Black Flag.
These missions provide the player with a specific target or group of targets, and task him with eliminating the target.
How the player eliminates the targets is typically up to them, although it can sometimes be specified as part of the contract or offered as an additional reward for killing the enemy in a certain way.
Targets for assassination can be located on islands, in port towns, or even on ships sailing the Caribbean.
It is best to wait to have the blow pipe to start tackling the Assassin Contracts. Still, most can be completed without it just it results in an increase in difficulty. You get a base Reward of 1,000 R with a bonus if you do not trigger open conflict.