Unlike their European predecessors in the experimentation with hallucinogens and aesthetics who undertook it as an exotic tradition brought from afar, many Latin American and North American authors turned to visionary practices and substances (cannabis, peyote, psilocybin mushrooms and ayahuasca, among others) as a main element of their own cultural heritage and territory. Though commonly restricted to the specific category of "psychedelia," the narratives in this corpus from the 20th century only acquire their true depth once included within a much vaster realm, that of visionary traditions, mostly originated in non-Western sources --with exceptions among divinators, witches and sorcerers in Europe -- both in the Old World of the Orient and Africa, but particularly in the New World, in America. Problematically blurring use and exchange value, the 20th century seized these substances as sources of forbidden pleasures which alienated laborers, while their prohibition generated immense fortunes that destabilized democracies throughout the continent, motivated violence, and funded mafias, guerrillas and paramilitary groups. Yet, visionary plants and practices spread with a transcultural power that even today allows for the survival of ethnic groups and traditional knowledge long hidden, while also feeding urban consumptions that generate innumerable subcultures, time and again misunderstood as a sign of decadence. In this dissertation these "underworld" practices are also manifestations of something prior and parallel to the birth of a culture of mass consumers: they mark an encounter between Indigenous, Afro, rural and mestizo influences in the voices of authors who contributed to culture from the margins of very hierarchical and racist societies, and assumed a leading role in their intellectual debate, capturing its mixtures, dark humor, conflicts and transculturations via writing and films. Initially marginalized in the low worlds of taverns, destitute neighborhoods, crime, prisons and prostitution venues, hallucination and hallucinogens--simultaneously a colonial anathema and a sacred pre-Columbian ritual of transcendence--survive and thrive, passing on to the urban minorities of artists and thinkers I will examine in this dissertation, now even including synthetics like Lysergic Acid Diethylamide (LSD). Late Avant-gardes between the 1950s and 1990s--beatniks, counterculture, yippies and Chicanos in the US, the Onda generation and the "jipitecas'' in Mexico, and the "nadaístas'' and the Cali group in Colombia--partially rescued this knowledge, but, above all, its consumptions, preserving some of them as an original heritage within their metaphysics, politics and aesthetics, and as a core part of many of their ideological and secular inquiries. Banned and misconstrued by the viceregal, republican, national and transnational elites, both in the colonial past, and in the contemporary moment of an hemispheric circuit -- within the geopolitics of Nixon‘s War on Drugs -- visionary and hallucinogenic uses continue shaping much of the cultural panorama of America today. The variety of films and texts observed in this project gives a measure of the true heterogeneity of Latin American and US authors of the 20th century: In their works we reconnect a fracture that divides not only two, but many worlds, while it makes possible, for once, to conceive the simultaneous reality of them all.