18th Street, also known as Calle 18, Barrio 18, Mara 18, or simply La 18 in Central America,is a multi-ethnic mostly hispanic transnational criminal organization that started as a street gang in Los Angeles. It is one of the largest transnational criminal gangs in Los Angeles, with 30,000 to 50,000 of members in 20 states across the US alone and is also allied with the Mexican Mafia.

18th Street gang started near 18th Street and Union Avenue in the Rampart District of Los Angeles. There is conflicting information as to the exact area, but this is a generally accepted area by most academic sources. They were originally part of Clanton 14 but wanted to make a separate "clique" called Clanton 18th Street and allow immigrants the opportunity to join. This proposal was rejected by the Clanton 14, which led to the formation of the 18th Street gang. The two gangs have been bitter rivals ever since.

The 18th Street gang grew by expanding its membership to other nationalities and races, and it was among the first multiracial, multi-ethnic gangs in Los Angeles. In the beginning, they were made up largely of second-generation Hispanics.

The majority of 18th Street cliques operate throughout Southern California, but are active in other states and internationally as well. Los Angeles members began migrating to other areas outside America and started to establish their own cliques. 18th Street cliques have been identified in 120 cities in 37 states and the District of Columbia in the United States, as well internationally in Spain, Australia, Canada, England, France, Germany, Lebanon, Peru, Philippines, Chile, Ecuador, Mexico, Guatemala, Honduras, and El Salvador.

18th Street gang members are required to abide by a strict set of rules. Failure to obey the word of a gang leader, or to show proper respect to a fellow gang member, may result in an 18-second beating, or even execution for more serious offenses. According to the FBI, some factions of the 18th Street gang have developed a high level of sophistication and organization.

18th Street gang members often identify themselves with the number 18 on their clothing and sporting clothing from sports teams such as the Duke Blue Devils, Los Angeles Clippers, Los Angeles Angels, Los Angeles Chargers, Los Angeles Dodgers, Los Angeles Lakers and Oakland Raiders. 18th Street will use the symbols XV3, XVIII, X8, 99 (9+9=18), and 3-dots in their graffiti and tattoos. 18th Street colors are blue and black; blue is to represent and to pay tribute to The Mexican Mafia, and black is to represent the original color for the gang. The 18th Street gang is occasionally referred to as the "Children's Army" because of its recruitment of elementary and middle-school aged youth.

They also allow other races to join their ranks making the gang Multi-ethnic. In El Salvador it is common for members of the gang to be tattooed on the face with a large "18". In many cases the tattoo covers the entire face.

"We recognize them as one of the most violent street gangs and one of the most prolific in the United States,"