Abstract. – In the 19th century Christian missionaries working in Western Canada invented new scripts to evangelize the Native American Indians of the region. If the circumstances of
the creation of the Cree syllabic writing by the Methodist James Evans are today well known, there is still a lack of knowledge concerning the factors that led the Catholic missionaries to develop new scripts as well. This paper presents for the first time two writing systems, the first syllabic, the second hieroglyphic, invented and propagated among the Dene by the Missionary Oblates of Mary Immaculate. After showing that both scripts were developed for an exclusive recitational use, a study of their semiotic features proposes to describe the necessary conditions for a graphic system to overcome the limits of its original context. [Canada, Dene, Cree, Blackfoot, missions of Western Canada, Anthropology of writing]