There are two different sorts of organizations on XMR, groups and factions. Groups are smaller or less formal gatherings of characters. They may be short-term or long-term, but are not as concrete as official factions. Players are welcome to start groups without staff permission. A wiki page may be created on the wiki, and it will be linked to the character pages (it should NOT be added to the teams listing). They may, however, create a wiki tag to use on logs and character pages. Players may request to have a group channel on the game.
Factions are long-term, large, official teams of characters, such as the Brotherhood and X-Men. They have full team support, which includes: a wiki page listed under the 'teams' menu, listing on +roster, malias, and a channel. Factions are generally created by staff. Player-made factions will be chosen from amongst successful groups that reach a large enough size and scope to warrant it.
Players may always belong to multiple factions and groups, provided these groups are not diametrically opposed (for example, one character cannot both be a Brotherhood member and a member of Xavier's School at the same time). However, the general rule is that a player may not have more than one alt per faction (for example, a player cannot have two active Morlocks characters at the same time).
Staff approval is needed to join or change factions, but group membership is left to the discretion of the players.