This review article highlights the role of microbiota in health and diseases, emphasizing its classification into gut, oral, respiratory, and skin microbiota. Microbiota are symbiotic with the host, contributing to homeostasis and immune function. However, dysbiosis can lead to various diseases, including cardiovascular diseases (CVDs), cancers, respiratory diseases, and chronic inflammatory conditions. The article discusses the current understanding of how microbiota links to host health and pathogenesis, focusing on the gut-brain axis, colonization resistance, and immune modulation in healthy conditions. It also explores the pathogenesis of microbiota dysbiosis in disease development, particularly through community composition changes, immune response modulation, and chronic inflammation. Finally, the article introduces clinical approaches that utilize microbiota for disease treatment, such as microbiota modulation and fecal microbial transplantation. The review underscores the importance of further research to understand the complex interactions between microbiota and the host, and to develop personalized medicine based on microbiome-based diagnostics.This review article highlights the role of microbiota in health and diseases, emphasizing its classification into gut, oral, respiratory, and skin microbiota. Microbiota are symbiotic with the host, contributing to homeostasis and immune function. However, dysbiosis can lead to various diseases, including cardiovascular diseases (CVDs), cancers, respiratory diseases, and chronic inflammatory conditions. The article discusses the current understanding of how microbiota links to host health and pathogenesis, focusing on the gut-brain axis, colonization resistance, and immune modulation in healthy conditions. It also explores the pathogenesis of microbiota dysbiosis in disease development, particularly through community composition changes, immune response modulation, and chronic inflammation. Finally, the article introduces clinical approaches that utilize microbiota for disease treatment, such as microbiota modulation and fecal microbial transplantation. The review underscores the importance of further research to understand the complex interactions between microbiota and the host, and to develop personalized medicine based on microbiome-based diagnostics.