Bacteria are single-celled microorganisms that are the simplest forms of life on Earth. Their characteristic feature is that they lack a nucleus and membrane-bound organelles, and typically have a cell wall composed of peptidoglycan. Actinobacteria are ubiquitous in various environments, displaying remarkable ecological diversity. They thrive in soil, water, and even extreme habitats like hot springs. Actinobacteria play crucial roles in nutrient cycling, decomposition, and soil health. These bacteria find extensive applications in various industries. Their enzymes play a critical role in biofuel production, waste treatment, and pharmaceutical synthesis. Their antibiotic properties make them valuable in combating infectious diseases and agricultural pests. This book provides comprehensive insights into the field of microbiology, especially with respect to phylum Actinobacteria. It unravels the recent studies related to the ecology, diversity and applications of Actinobacteria. This book includes contributions of experts and scientists, which will provide innovative insights into this field.