The intestinal microflora, often referred to as a "forgotten organ," plays a crucial role in maintaining health and influencing the development of the mucosal immune system. The flora's metabolic activity is comparable to that of a virtual organ, and its collective influence on mucosal homeostasis and immune responses is beginning to be understood. The composition and structure of the gut flora are shaped by natural selection at both microbial and host levels, promoting mutual cooperation and functional stability. Commensal bacteria exert protective, structural, and metabolic effects on the intestinal epithelium, and their presence is essential for maintaining a healthy gut environment. However, in genetically susceptible individuals, some components of the flora can contribute to the pathogenesis of various intestinal disorders, including inflammatory bowel diseases. Manipulating the flora to enhance beneficial components represents a promising therapeutic strategy. Understanding the complex interactions between the host and the gut flora is crucial for developing effective treatments for infectious, inflammatory, and neoplastic diseases.The intestinal microflora, often referred to as a "forgotten organ," plays a crucial role in maintaining health and influencing the development of the mucosal immune system. The flora's metabolic activity is comparable to that of a virtual organ, and its collective influence on mucosal homeostasis and immune responses is beginning to be understood. The composition and structure of the gut flora are shaped by natural selection at both microbial and host levels, promoting mutual cooperation and functional stability. Commensal bacteria exert protective, structural, and metabolic effects on the intestinal epithelium, and their presence is essential for maintaining a healthy gut environment. However, in genetically susceptible individuals, some components of the flora can contribute to the pathogenesis of various intestinal disorders, including inflammatory bowel diseases. Manipulating the flora to enhance beneficial components represents a promising therapeutic strategy. Understanding the complex interactions between the host and the gut flora is crucial for developing effective treatments for infectious, inflammatory, and neoplastic diseases.