Street gangs have the following common characteristics: territoriality, usually based on common residence; versatility in offense patterns; a preponderance of male members; a preponderance of racial or ethnic minority membership; ages that range from pre-teens to the thirties; location in inner-city areas or areas with significant social problems; and members who are generally oriented toward criminal activity. Excluded from the street gang category are prison gangs, terrorist gangs, motorcycle gangs, organized crime groups, and many youth groups or cliques that occasionally get into trouble with the law, but for whom delinquency is incidental to their social focus. Less easily dismissed from the street gang category are drug- distribution gangs, tagger crews, and some Asian-American gangs that differ in several respects from other street gangs. Most important for intervention and prosecution purposes is the distinction between street gangs and drug gangs. The latter are specialists in offending, older in age on average, more cohesive, more tightly and hierarchically led, far smaller, and more demanding of members' loyalty than street gangs. With special laws, special prosecution procedures, and special police experts, the prosecution's general theme in gang cases is simple and straightforward: prove the defendant's gang affiliation and thereby increase the likelihood of conviction and of sentence enhancement. Gang membership per se is taken as evidence of guilt and of commitment to a career of crime. Whereas the prosecution uses the defendant's gang affiliation to show culpability, the defense often uses it as a mitigating factor, suggesting that peer pressure from gang membership compelled the criminal behavior. Expert testimony should be available to both prosecution and defense, based on criminological research, to ensure that the portrayal of a specific gang member in court matches with the actual gang characteristics and behavior on the streets.