S.T.A.L.K.E.R.: Shadow of Chernobyl/Factions

Army
They guard all roads in the zone, control perimeters, hunt mutants and shoot looters (Stalkers) down.
 * Attitude:	 Hostile
 * Affiliations:    None
 * Joinable: No

Mobile Science Lab (MSL)
A mobile lab that resembles a small heavily armored bunker with small tainted glass windows. It has its own life-support and so can work autonomously for several months.
 * Attitude:        Neutral
 * Affiliations:    Duty. If Duty is your enemy the MSL will also be hostile
 * Joinable: No

Monolith
This group displays many features of a religious sect. It's members believe in an complex alien crystal, the Monolith, somewhere deep in the middle of the zone.
 * Attitude: 	 Hostile
 * Affiliations: 	 None
 * Joinable: No

Duty
A paramilitary group known for it's discipline, whose Members live according to a strict code.
 * Attitude:        Neutral
 * Affiliations:    MSL
 * Joinable: Yes

Bandits
Members of the Criminal underworld who came to the zone for various reasons, to make money, to sell Artifacts or to hide from the law.
 * Attitude:        Hostile
 * Affiliations:    None
 * Joinable: Only in Clear Sky

Military Stalkers
Soldiers who underwent a special training in the Zone or Stalkers who voluntarily signed a contract with the army.
 * Attitude:        Hostile
 * Affiliations:    Army
 * Joinable: No

Mercenaries
The most clandestine and secretive faction in the zone, some don't even believe in its existence.
 * Attitude:        Hostile
 * Affiliations:    None
 * Joinable: No

Lone Stalkers
Lone stalkers who expore the zone on their own, they are not part of any faction, neither Duty, nor Freedom. Most Stalkers work this way since being part of a group takes time and more importantly loot.
 * Attitude:        Neutral
 * Affiliations:    None
 * Joinable: Yes (You are one from the Beginning of the game)

Freedom
Anarchists and daredevils who declare themselves fighters for free access to the zone and consequently find themself in constant conflict Army, Military stalkers, and the Duty faction.
 * Attitude:        Neutral
 * Affiliations:    None
 * Joinable: Yes