The investigation and prosecution of gang cases carry many difficulties, such as recanting witnesses, intimidated bystanders, and unsympathetic victims. Other challenges include explaining motive and theories of liability. In order to assist prosecutors, this monograph addresses key pre-trial and trial issues in the context of gang evidence. An overview is provided of a typical gang case, with an emphasis placed on the use of gang evidence in the courtroom. Courts continue to sanction broader uses for gang evidence, such as for proving intent, motive, identity, criminal liability, and to explain witnesses conduct. The way in which gang evidence can be used to accomplish each of these purposes is examined in turn and the use of gang evidence is highly suggested in any case involving gangs. Once gang evidence is established as crucial to a case, a plethora of useful information about gangs can be demonstrated. Gang experts can be brought in to illuminate why gang members join gangs, as well as the importance of territoriality to a gang and the relationships among drugs, money, guns, and territory. Next, the author considers the steps prosecutors should take to prepare the court for the admission of gang evidence, including informing the defense of the prosecution's intent to introduce gang evidence and presenting the court with a brief outlining the intent to introduce gang evidence and the reasons for it. Witness problems in gang cases are explored and California's Street Terrorism Enforcement and Prevention (STEP) Act is described. STEP was enacted in 1988 and amended in 2000 to substantially increase sanctions for gang crimes. Thus, in California, any felony or misdemeanor committed for the benefit of, in association with, or at the direction of a criminal street gang is subject to enhanced punishment. Next, the discussion focuses on getting the most out of a gang expert in court. Any expert must have an intimate and working personal knowledge of the defendant's gang and must appear credible. Case examples throughout the monograph illustrate key points.