 Gut microbiota play important roles in the body, and their composition and diversity can influence various diseases. The host promotes a healthy gut microbiome by releasing specific and non-specific factors that encourage certain bacteria to grow while inhibiting others. Diet, antibiotics, and age can alter gut microbiota, and studies have linked imbalances in the microbiome to several diseases. This review discusses how the host shapes its gut microbiota through specific and non-specific factors, how environmental and nutritional factors affect it, and ways to modulate the balance using prebiotics, probiotics, and fecal microbiota transplantation.