A prison gang[1][2] is an inmate organization that operates within a prison system, that has a corporate entity, exists into perpetuity, and whose membership is restrictive, mutually exclusive, and often requires a lifetime commitment.
Skarbek observes that in a small, homogeneous environment, people can use social norms to interpret what behavior is acceptable, but a large, heterogeneous setting undermines social norms and acceptable behavior is more difficult to determine.
[4] Skarbek suggests prison gangs function similar to a community responsibility system.
In some circumstances, prison gangs "outgrow" the internal world of life inside the penitentiary, and go on to engage in criminal activities on the outside.
Thus, gangs are often more-or-less tolerated by prison administrators due to the side-benefits they afford.