An ethnobotanical study was performed of the ferns and lycophytes used by the Guaraní of Misiones Province, Argentina. It was determined that fifty species are used, and details of the uses and the Guaraní names and nomenclature are given and discussed. Fern and lycophytes are used for medicines, crafts, in magic rituals, and marketing of the plants. The most important traditional use of ferns is for medicine and the most important modern use is commercialization for use in horticulture.