Résumé : Biodiversity is among the richest treasures of the earth. Despite their small size, microbes play a vital role in environmental monitoring and making the earth sustainable. Microorganisms preserve and assist plants and animals o either directly or indirectly, and, due to their omnipresence in nature, they inhabit conditions such as extreme temperatures, water, soil, salt, medical wastes, agricultural wastes, and air.Microbes are also important in human culture and play an essential role in existence of life. They are present in food fermentation, sewage treatment, medical, agricultural, and soil waste, antibiotics, soil fertility, model organisms, and human microbiota, aid with decomposition, and are responsible for infectious diseases. This volume represents an important contribution to the field, highlighting the importance of microbial biodiversity to society.