Our bodies are made up not only of human cells but also of trillions of microorganisms that make up the human microbiome. These microbes, bacteria, viruses, fungi, and archaea, are on our skin, in the gut, in mucosal surfaces. The microbiome was once considered a mere collection of commensal microbes but is now held in such high regard like an “invisible organ” because of its major effects on human health and diseases.If we look at it from the microbe’s point of view, it is the gut microbiota that has drawn the most attention by far. Consisted mainly of two bacterial phyla Firmicutes and Bacteroidetes, these bacteria have an essential part in the digestion process, especially the fermentation of the complex carbohydrates and production of the vitamins such as vitamin K, B12. In addition to this, they regulate the immune system development and functioning by training it to react correctly to harmful microbes and harmless antigens.Moreover, the microbiome fortifies the host against microbial invasions. This idea known as colonization resistance involves beneficial microbes competing with pathogens for nutrients and sites of attachment. When the balance is compromised, the state called dysbiosis may be involved in the pathogenesis of various diseases such as inflammatory bowel disease, obesity, diabetes and even the dysfunction of mental health through the gut-brain interaction.FMT (fecal microbiota transplantation), by far the most potent microbiome-based new medicine, has generated stunning results in patients with recurrent Clostridioides difficile infections. It uses a healthy donor’s feces to revivify the microbial flora of the patient’s gut.Nevertheless, elements of modern living such as unhealthy eating, stress, antibiotic overuse and the like can disrupt the microbiome. Antibiotics though crucial for saving lives may sometimes lead to disturbance of the beneficial members of the microbiome with subsequent long-term effects.To sum up, the human microbiome stands as a necessary part of our physiological make-up by affecting our nutrition, immune function and general health.