The Cajón in Cuba is both music and a possession ritual. The combined approach of musicology and religious anthropology highlights the specificities of the Cajón. Therefore, it is possible to position the musical and ritual practice of Cajón among different Afro-Cuban cults in Havana. Considering the Cajón as total social fact, this research aims to analyze the complexity of ritual taking into account social, musical and religious aspects. The analysis shows that the Cajón can be recognized in different way among religious practices of Afro-Cuban cults, even sometimes coming out of its framework. The Cajón covers a sequence of rituals (Misa, Biagué, Chamalongo, sacrifice and Toque) embedded in a sacred space where every participant has a well-identified role. The analysis of one sequence of ritual and of interactions which happen enables the definition of the role of music. The music is permanently adapting to the ritual being one of its components: it structures the ritual time, it participates to the introduction and also to the socialization of the possession trance. The musicians as participants use in creative way melodic systems and rhythmic patterns associated to the music of rumba, makuta and palo monte. Overlapping of repertoires and musical systems generates a complexity concerning sound effects. We conclude that the musical analysis is a key for the understanding of the ritual.