Microbiome is a term that describes the genome of all the microorganisms, symbiotic and pathogenic, living in and on all vertebrates. The gut microbiome is comprised of the collective genome of microbes inhabiting the gut including bacteria, archaea, viruses, and fungi. Information about these microbes living in our guts is growing at a tremendous rate. Till recently, heterogeneity among human populations was attributed to various allelic forms of genes. The human intestine harbors trillions of bacteria which constitute more genome than all the human cells in the body. The distribution of microbes is spatial in the gut, with the colon containing the largest diversity and abundance of microorganisms. The colon also harbors more aerobes than the small intestine, owing to its proximity to the environment. Humans have coevolved with the commensals and maintain a symbiotic relationship. Intestinal microbes out-compete the pathogens and maintain the integrity of the epithelium which may be a key factor in preventing inflammation. Diverse microbial communities are essential for maintaining the intestinal ecosystem and play a vital role in harvesting energy from foods and producing micronutrients. In return the microbes receive food and a suitable environment for growth.