Pachucos are Mexican-American youths who developed their own subculture during the 1930s and 1940s in the Southwestern U.S. , particularly in L.A.They wore distinctive clothing (such as zoot suits) and spoke their own dialect  called “caló” or Pachuco. Due to their double marginalization stemming from their youth and ethnicity, there has always been a close association and cultural cross-pollination between the Pachuco subculture and gang subculture.

The Pachuco style originated in El Paso, Texas and Ciudad Juarez Mexico and moved westward, following the line of migration of Mexican railroad workers “traqueros”") into Los Angeles, where it developed further. The word "pachuco" originated, probably early in the 20th century, in a Mexican Spanish slangterm for a resident of the cities of El Paso and Juárez. Even today, El Paso and Juárez are the "El Chuco Town" or "El Pasiente" by some.

Another theory is that the derivation of the word "pachuco" came from Pachuca, the name of the city in the Mexican state of Hidalgo where Mickey Garcia, thought by some to be the originator of the zoot suit, befriended a local of the town known as "El Hueso". El Hueso was an elderly man known only to have a tatoo on his right shoulder. It is unknown what the tattoo said but some have claimed that it bore two names: one beginning with a "J" and the other with a "B". Mickey Garcia brought his style from Pachuca, Mexico toSan Diego. Another theory says that the word derives from pocho, a derogatory term for a Mexican born in the United States who has lost touch with theNMexican culture. The word is also said to mean "punk" or "troublemaker".

Another theory is put forth by Cummings, 2009 (see references), who postulates a possible indigenous origin of the term.

The Mexican comedian and film actor Germán Valdés, better-known by his artistic name "Tin-Tan", popularized Pachuco dress and slang to the Mexican population through his films during the Golden Age of Mexican films. The influence of Valdés is responsible for the assimilation of several Caló terms into Mexican slang.

The Mexican Nobel Laureate, Octavio Paz writes in the essay, "The Pachuco and Other Extremes" that the Pachuco phenomenon paralleled the zazou subculture in World War II-era Paris in style of clothing, music favored (jazz, swing, and jump blues), and attitudes, although there was no known link between the two subcultures.

The pachuco subculture declined in the 1960s, evolving into the Chicano style. This style preserved some of the pachuco slang while adding a strong political element characteristic of the late 1960s American life.

In the early 1970s, a recession and the increasingly violent nature of gang life resulted in an abandonment of anything that suggested dandyism. Accordingly, Mexican-American gangs adopted a uniform of T-shirts and khakis derived from prison uniforms, and the pachuco style died out. However, the zoot suit remains a popular choice of formal wear for urban and rural Latino youths in heavily ethnic neighborhoods. It is typically worn at a prom, or in some cases, at informal Latino university commencement ceremonies.

Pachucos called their slang Caló (sometimes called "pachuquismo"), a unique argot that drew on the original Spanish Gypsy Caló, Mexican Spanish, the New Mexican dialect of Spanish and American English, employing words and phrases creatively applied. To a large extent, Caló went mainstream and is one of the last surviving vestige of the Pachuco, often used in the lexicon of some urban Latinos in the United States to this day.

The same word "pachuco" is used in Costa Rica to define Costa Rican slang. It nevertheless differs from the Mexican slang. In Costa Rica the term "pachuco" refers to a vulgar or indecent person.

 La Pachuca

The "Pachuca", the female counterpart of the Pachuco, had as strong an aesthetic sensibility as the male zoot suiter. The Pachuca's hairstyle tended to be a high "coif" (a more pronounced version of the typical hair style of the time), sometimes using hair grease. Her makeup was heavy, particularly the lipstick. The preferred color of clothing was black. One very loud version of the Pachuca look entailed wearing the masculine zoot suit, albeit with modifications to fit the female form. This was very subversive at the time because of long-held gender roles that dictated how a person should dress. Another variation included full, knee-length skirts with the standard zoot suit finger-tip jacket. Sometimes, she donned the standard heavy gold pocket chain.

This style was associated with gang membership and activity. The idea of gang membership and gang activity came from the Zoot Suit riots that took place mainly in Southern California.The negative image of the male zoot suiter as a "violent gangster" naturally extended to the Pachuca as well. The promiscuous image came from contravening the traditional "see and be seen" fashion aesthetic — the Pachuca's high public visibility during a time when the "good" [minority] woman belonged in the home was seen in a scandalous light.

The Pachuca's challenge to the dominant perception of femininity came during the period between the advent of women’s suffrage in 1920 and the upsurge in feminist activism of the 1960s and 1970s.