Street gangs are defined as a group of individuals, usually youth, banded together under a common identity for the purpose of carrying out persistent illegal activity. This activity may revolve around dealing narcotics, robbery, pimping, burglary, racketeering, extortion, vandalism, and the hostile defense of their turf from other gangs. The sorting and cataloging of gang members and the study of street gang culture is a whole branch of criminology all in itself.

The knowledge of street gang activity amongst the municipal police is often so intimate that they can read graffiti messages and know the street names and specialties of each member. Frequently they keep their ear cocked for activity within their neighborhood, and understand the significance of events in a light that makes little sense to those who don't follow gang activities.

In North America, the primary cities which have significant gang activity are Los Angeles, Chicago, Houston, St. Louis, and Detroit. However, any major city may play host to a gang.

Much research is done to study what conditions give rise to gangs. Most experts agree that the causes are a combination of impoverished neighborhoods, racial minorities, troubled homes, and youths who don't fit in. Young men especially join street gangs to prove their machismo, give themselves a community sense of identity, defy authority within the "system", and compensate for low self-esteem and feelings of being an outsider.

The associative signs of identity will vary in form but always be present. The gang members might wear clothing which matches in style, color, or detail, have the same tattoo, same hairstyle, or even a common piece of jewelry. Most gangs have a designated turf, which is their home area, or other places which they claim as their own, and also have an identifiable organization or hierarchy. Usually the leader will simply be the currently most senior member, and a pecking order chains down from there. It is also somewhat common for a gang to be based on a common idea of hatred for other ethnic groups or religions, or promotion of their own race or religion.

Some speculation has suggested that street gangs are also a natural byproduct of the inherent short-comings in any society. Particularly, gang members seem to crave structure. While they reject the rules of society they have their own tight, unbreakable code. While they disdain conforming to society, they will adhere to their own dress code. They have their own value system and honor code. Street gangs may simply be the underprivileged providing their own structure and order when they perceive chaos and disorganization elsewhere.

In dealing with a gang as a law enforcement professional, the best policy is to seek the mentoring of a peer who knows the gang's history. Once in the presence of a familiar authority figure, a gang member may be more cooperative, as long as you aren't asking them to rat out another member. It is because their allegiance is always stronger within their group than it ever will be to anyone else, a gang member's word should never be trusted until you know all the facts surrounding a given case.

In some cases, gangs have become so strong that the influence of the police is effectively dulled. there are sections of divisions in Los Angeles, for instance, where police officers simply will not go unless it's in force, with a whole convoy of squad cars going in at once. At this point, the line between a street gang and a terrorist organization grows very thin. A separate issue is the other varieties of gangs, such as prison gangs and biker gangs. Street gangs might become prison gangs when all the members are incarcerated at the same time, but mainly prison gangs form within prison by the association of previously unconnected individuals.

The Internet has given rise to a new, far more dangerous development, which is the formation of international street gangs. While it was previously a rare thing for gangs to have affiliations outside of their own few city blocks, today there are dozens of gangs with members in several cities and countries throughout the world. amongst others, they are tracked closely by the FBI. The parallel rise of international organized crime is no coincidence with this, and indeed connections between Internet crime and street crime with a common gang identity have been discovered.

It may be unsettling to think that what used to be a handful of rough boys in a neighborhood is now an international organization with it's own web pages, but it's an idea we all have to face. This kind of takes the zip out of all those "cyberpunk" novels we were reading back in the 1980's when we were imagining what the new wired world would be like. It turns out the cyberpunk universe carries it's own problems from the street punk universe... and isn't nearly as much fun as we thought it would be.