We will therefore focus on the ritual uses of hallucinogens, asking two questions. On the one hand, the causality. What determines ritual hallucinogenic experience? We will show that we need to move from the look of substances to ritual devices that are the true control frameworks for hallucinogenic experience. On the other hand, the question of meaning. What does and what is practically the ritual hallucinogenic experience? We will show that it is a technique of communication and knowledge, that it vehicles worlds. This theoretical course will also be an opportunity to question some of the most classic concepts of anthropology, such as culture and determinism, rite and symbolic efficiency, technique and physical efficiency.