The study of the human microbiome has seen an explosive growth in the past decade, primarily driven by advances in sequencing technologies and computational resources. The microbial cells that colonize the human body, including intestinal and skin environments, are at least as abundant as our somatic cells and contain a much greater number of genes than the human genome. However, different people harbor radically different collections of microbes and we do not yet understand how the variation within a person over time or that between different people influences wellness, the preservation of health or the risk for or onset of disease. Experimental studies reveal possible patho-physiologies linked to abnormalities in the microbiome such as cancer, diseases of the skin, metabolism, malnutrition, food allergies, autoimmune and psychiatric disorders.