This study will discuss the foundations and development of the short story of effect, or cuento de efecto, in the River Plate region (Argentina and Uruguay). This subgenre of the fantastic short story was first popularized widely among readers of periodicals and writers in the first decade of the twentieth century by Leopoldo Lugones (Argentina). Readers in the River Plate area were already familiar with the work of French- and English-language writers of fantastic tales like Jules Barbey d’Aurevilly, Edgar Allan Poe, Jean-Marie Villiers de l’Isle Adam, and Guy de Maupassant, and Lugones’s continuation and elaboration of the same type of literature was eagerly received in Buenos Aires. Lugones encouraged other local writers to expl...