Life on Earth harbours an unimaginable diversity of microbial communities. Among these, gut microbiome, the ecological communities of commensal, symbionts (bacteria and bacteriophages) are a unique assemblage of microbes. This microbial population of animal gut helps in performing organism's physiological processes to stay healthy and fit. The role of these microbial communities is immense. They continually maintain interrelation with the intestinal mucosa in a subtle equilibrium and help the gut for different functions ranging from metabolism to immunologic functions like upgradation of nutrient-poor diets, aid in digestion of recalcitrant food components, protection from pathogens, contribute to inter-And intra-specific communication, affecting the efficiency as disease vectors etc. The microbial diversity in the gut depends upon environmental competition between microbes, their sieving effects and subsequent elimination. Due to wide diversity of anatomy and physiology of the digestive tracts and food habits, the gut microbiome also differs broadly among animals. Stochastic factors through the history of colonization of the microbiome in a species and in situ evolution are likely to establish interspecies diversity. Moreover, the microbes offer enormous opportunity to discover novel species for therapeutic and/or biotechnological applications. In this manuscript, we review the available knowledge on gut microbiome, emphasising their role in health and health related applications in human. © 2017 Soumya Chatterjee et al., published by De Gruyter Open 2017.