This book contains eight chapters that detail biofertilizers. Chapter One discusses arbuscular mycorrhizal (AM) fungi, known to form symbiotic associations with most of the crop plants important in agriculture, horticulture and forestry. Chapter Two critically examines the current state-of-art use of zinc solubilizing bacteria strains as biofertilizers and the important roles performed by these beneficial microbes in maintaining soil fertility and enhancing crop productivity. Chapter Three presents Burkholderia, an important bacterial species that directly promotes plant growth. Chapter Four investigates the role of different phosphorus sources on phosphorus bioavailability and explores its cycling in both plants and soil, while also exploring its effects on plant growth and agricultural production. Chapter Five describes the multifaceted environmental impact of microbially treated insoluble inorganic natural sources. Chapter Six discusses the importance of iron (Fe) in soil and plants, the factors affecting its solubility and deficiency in the soil, and the potential of microbial iron solubilizers as a sustainable approach to enhancing Fe availability in soil, and promoting plant growth. Chapter Seven focuses on Azotobacters and assesses their diversity, action mechanisms, ecological significance and its biotechnological applications. Lastly, Chapter Eight discusses the role of biofertilizers in sustainable agriculture.