Perhaps no science topic has taken human health by storm over the past 15-20 years quite like the microbiome. The collection of living organisms—bacteria, viruses, fungi—that have made their home in and on our bodies have piqued the attention of the public, scientists and journalists, alike. Scientists have linked the microbiome—and changes in its composition—to a wide range of maladies: from obesity to asthma to mental disorders like depression. Many now refer to the microbiome as a human organ—on par with our stomach and heart! This hype has led to the commercialization of a variety of products–such as probiotics—and procedures that claim to will establish and maintain a healthy microbiome. While there have been some fascinating studies with ‘germ-free mice’ (which lack a microbiome), scientists still aren’t sure what constitutes a healthy human microbiome—or if one even exists. While the microbiome is not an epigenetics topic, the Epigenetics Literacy Project has decided to cover the microbiome because like epigenetics the microbiome involves potential changes to our health that are not hard-coded into our genomes.