This special issue of Trends in Organized Crime on the ‘Mexican Cartels’ brings together contributors from academic, policy, military, security consulting, and investigative reporting backgrounds with some currently, or in the past, engaged in overlapping professional roles. The topic is of significance because these groups have developed from drug trafficking organizations to transnational criminal entities operating not only in Mexico but increasingly in Central America, throughout the United States, and in other regions of the Western hemisphere, West Africa, and Asia. It is important to understand this process and to remember that Mexico did not always have cartels. Since their initial appearance in the late 1980s, they have greatly evolved with the preferred narcotics route into the US shifting from Southern Florida to over the US border via Mexico and with the subsequent dismantling of the major cartels found in Colombia in the 1990s. Cartel evolution has been influenced by numerous factors ranging from intentional and unintentional governmental policies and second order effects, through changes in illicit market preferences and flows, to cartel mergers, infighting, and innovations. Typically, forgotten events that have directly impacted the rise of cartels include the torture killing of DEA agent Enrique “Kiki” Camarena in Mexico in 1985, US counter-narcotics efforts spearheaded by the DEA to track down those responsible, and the initial establishment of the ‘plaza system’by Miguel Ángel Felix Gallardo (“El Padrino”) in the 1987–1989 era as a defensive countermove against those efforts. The process of political transition in Mexico from an autocratic—seventy-year one party dominated system under the Partido Revolucionario Institucional (PRI)—to a democratic multiparty system beginning in 2000 further greatly influenced cartel evolution. Under the PRI, the major cartels in Mexico, each with their assigned territories (plazas) remained subordinate to a state whose officials and elite families quietly profited from the illicit narcotics trade. This relationship with the state drastically changed with the election of two Partido Acción Nacional (PAN) administrations under Vincente Fox (2000–2006) and then Felipe Calderón (2006–1012).