The gut of humans harbors a multifarious and dynamic population of microorganisms, known as gut microbiota. This microbial ecosystem is crucial for preserving human health through diverse functions, including nutrient metabolism, immune system development, and protection against pathogens. Prebiotics and probiotics are known to preserve a healthy microbiome. The community of microbes inhabiting the digestive tract is recognized as a metabolic powerhouse actively influencing the host’s overall metabolism, contributing significantly to the digestion of food, nutrient absorption, and the production of essential metabolites. The microbiota of the gut has a multifaceted role in health and illness, and any imbalance or changes in the gut composition could contribute to disease pathogenesis. A balanced gut microbiota, its specific microbial compositions, and functional activities are referred to as eubiosis or equilibrium. While eubiosis is associated with overall well-being and health, any disruptions in this equilibrium (termed dysbiosis) caused by biotic or abiotic factors can alternatively lead to a number of chronic illnesses, comprising inflammatory bowel disease, type 2 diabetes, obesity, cardiovascular diseases (CVDs), and neurodevelopmental disorders. Understanding the intricate association existing among the gut microbiota and the host health paves the way for innovative diagnostic and therapeutic strategies targeting this critical microbial ecosystem. Recent advancements in artificial intelligence (AI) have revolutionized the study and application of gut microbiota. In this chapter, we describe the key roles of gut microbiota, emphasizing the role of eubiosis and dysbiosis in health and illness.