A covenant is a faction that a player may join in Dark Souls. Being part of a covenant grants various benefits, though it also imposes certain rules on the player. Breaking said rules can lead to negative effects. Covenants may also have an effect on the player's online interactions.
There are nine covenants in all. Some covenants have four ranks, from 0 to +3. Ranking up in a covenant can bring additional rewards.
Attacking or killing covenant members counts as a betrayal, resulting in expulsion.
Players may only join one covenant at a time. Should players wish to join a different covenant, it is necessary to break their contract with their previous covenant first, either through betrayal or through Oswald, the pardoner. The latter is highly recommended as doing so has less repercussions, while the former can cause several problems, such as being unable to rejoin the covenant until the player's sins are pardoned for a hefty price.
Upon leaving a covenant, even with the Oswald method, half of the progress the player has made in ranking up in the covenant is lost, should they wish to rejoin later. For example, a rank requiring 20 humanity will be reduced to 10 if one should rejoin and want to attain the previously held rank.