There are numerous studies of shamanism, but almost nonexistent monographs that directly address what shaman or shaman does, why and why do it. Based on six years of field work among a group of shamans, both native to the Amazon and Andean regions and Spanish trained in the tropical rainforest, Santiago López-Pavillard offers a novel approach to an implicated anthropology in which ethnographic description, theoretical debate on concepts and methods and experiential reflection on ethnographic practice and its effects on the researcher are intertwined. All this allows him to develop a reconceptualization of the shaman’s figure and shamanic practice around the ceremonial use of ‘master plants’, such as ayahuasca and tobacco, from which he builds a criticism of the disciplinary paradigms of social and cultural anthropology, and from which he also raises a very topical debate on the nature and scope of scientific knowledge in general. Shamans, ayahuasca and healing shows a particularly complex aspect of our society, such as the coexistence of various rationalities that obey different conceptions of reality. This requires clearly distinguishing a set of notions, such as health/healing, religion/spirituality or religious beliefs vs. spiritual knowledge, from which to try to understand how and why a progressive introduction of animist conceptions into Western society is given.