Resumen: In this article, the history of the microbiota is reviewed and the related concepts of the microbiota, microbiome, metagenome, pathobiont, dysbiosis, holobiont, phylotype and enterotype are de ned. The most precise and current knowledge about the microbiota is presented and the met- abolic, nutritional and immunomodulatory functions are reviewed. Some gastrointestinal diseases whose pathogen- esis is associated with the intestinal microbiota, including in ammatory bowel disease, irritable bowel syndrome and celiac disease, among others, are brie y discussed. Final- ly, some prominent and promising data with regard to the fecal microbiota transplantation in certain digestive illness are discussed. Idioma: Inglés DOI: 10.17235/reed.2017.4947/2017 Año: 2018 Publicado en: Revista española de enfermedades digestivas 110 (2018), 51-56 ISSN: 1130-0108 Factor impacto JCR: 1.858 (2018) Categ. JCR: GASTROENTEROLOGY & HEPATOLOGY rank: 70 / 84 = 0.833 (2018) - Q4 - T3 Factor impacto SCIMAGO: 0.524 - Medicine (miscellaneous) (Q2) - Gastroenterology (Q2)