Yeasts are essential actors in various fields and the interest they arouse today is due to their tremendous biodiversity, their polymorphism, their eukaryotic cell structure, their mode of reproduction and their physiology. They represent the micro-REZKI Meriem Amina, Doctor in Biotechnology, teacher-researcher at the University of Oran 1 in Algeria for over 23 years. I have supervised several students in master and doctorate with publications and I participated in the organization of various scientific events at the level of our university.organisms the most exploited by the man in the field of the pedagogy and the research, as well as the industrial field like the agroalimentary, the chemical industry, pharmaceutical and cosmetic. Their use deserves to have a thorough knowledge of all these characteristics and this is what is treated in this book that has gathered all the knowledge on yeasts supported by examples and references to facilitate research for students, researchers, technicians and engineers of laboratories.