The human intestine hosts a complex bacterial community called the gut microbiota. The microbiota is specific to each individual despite the existence of several bacterial species shared by most adults. Scientific studies reveal its influence on human health and diseases. In particular they have shown that the intestinal microbiota can play a causal role in the development of obesity and associated metabolic disorders, leading to the identification of different mechanisms. In humans, differences are observed in the composition of the microbiota, in the functional genes and in the metabolic activities between obese and lean individuals, that suggest a contribution of the microbiota to these phenotypes. Finally, the evidence linking intestinal bacteria to host metabolism could allow the development of new therapeutic strategies based on the modulation of the intestinal microbiota to treat or prevent obesity [155].