A growing body of evidence highlights the importance of the gut microbiota in early life. With technical advancements, we are yet to uncover our natural history by accounting for the vast diversity of microbial life which colonizes the human body. The word microbiota represents an ensemble of microorganisms that resides in a previously established environment. Gut microbiota (formerly called gut flora) is the name given today to the microbe population living in our intestine. One third of our gut microbiota is common to most people, while two thirds are specific to each one of us. In other words, the microbiota in our intestine is like an individual identity card.