The Mexican Mafia, also known as La eMe, is a Mexican American criminal organization in the United States. Despite its name, the Mexican Mafia has no origins in Mexico, and is entirely a U.S. criminal prison organization. Law enforcement officials report that the Mexican Mafia is the deadliest and most powerful gang within the California prison system.

Mara Salvatrucha, commonly known as MS-13, is an international criminal gang that originated in Los Angeles, California, in the 1980s. Originally, the gang was set up to protect Salvadoran immigrants from other gangs in the Los Angeles area. Over time, the gang grew into a more traditional criminal organization. MS-13 has a longtime rivalry with the 18th Street gang.