The human gastrointestinal (GI) tract harbors a complex and dynamic population of microorganisms, known as the gut microbiota, which play a crucial role in maintaining immune and metabolic homeostasis and protecting against pathogens. The composition and diversity of the gut microbiota are influenced by various factors, including diet, mode of delivery, and life events such as illness and antibiotic use. The gut microbiota is not as diverse as other microbial communities but exhibits functional redundancy, allowing for similar protein or metabolite profiles despite differences in microbial composition. The development of the gut microbiota begins from birth and is shaped by environmental and host factors. The gut microbiota is stratified along both transverse and longitudinal axes, with different regions supporting distinct microbial communities. Diet, particularly the availability of microbiota-accessible carbohydrates (MACs), significantly influences the gut microbiota. Intestinal mucus provides a source of carbohydrates for the gut microbiota and is crucial for maintaining gut health. The gut microbiota also plays a vital role in maintaining epithelial integrity, synthesizing essential vitamins, and regulating the immune system. Dysbiosis, characterized by altered microbial composition, has been associated with various inflammatory diseases and infections. Understanding the mechanisms linking the gut microbiota to health and disease is essential for developing therapeutic strategies to restore symbiosis and improve host health.The human gastrointestinal (GI) tract harbors a complex and dynamic population of microorganisms, known as the gut microbiota, which play a crucial role in maintaining immune and metabolic homeostasis and protecting against pathogens. The composition and diversity of the gut microbiota are influenced by various factors, including diet, mode of delivery, and life events such as illness and antibiotic use. The gut microbiota is not as diverse as other microbial communities but exhibits functional redundancy, allowing for similar protein or metabolite profiles despite differences in microbial composition. The development of the gut microbiota begins from birth and is shaped by environmental and host factors. The gut microbiota is stratified along both transverse and longitudinal axes, with different regions supporting distinct microbial communities. Diet, particularly the availability of microbiota-accessible carbohydrates (MACs), significantly influences the gut microbiota. Intestinal mucus provides a source of carbohydrates for the gut microbiota and is crucial for maintaining gut health. The gut microbiota also plays a vital role in maintaining epithelial integrity, synthesizing essential vitamins, and regulating the immune system. Dysbiosis, characterized by altered microbial composition, has been associated with various inflammatory diseases and infections. Understanding the mechanisms linking the gut microbiota to health and disease is essential for developing therapeutic strategies to restore symbiosis and improve host health.