Microbiomes exist in various niches of the human body and play some known and likely many unknown roles in human health and disease. Nearly two decades of research have laid the groundwork for this field, and we are now at a point where sophisticated tools and cutting-edge approaches can be applied to the microbiome to build models, understand mechanisms and ultimately impact medicine. This meeting will address important gaps in our knowledge as it relates to (Aim 1) understanding the microbiome in an ecological context, (Aim 2) dissecting the mechanisms by which microbes and microbial products modulate microbial and host biology, and (Aim 3) important new clinical breakthroughs in microbiome science. Anticipated outcomes of the meeting include enhancing international collaborations, providing exposure to unpublished microbiome research, exposing trainees to a broad range of science and potential future mentors, and giving trainees an opportunity to present their work in poster and oral formats in an international conference. This meeting innovates by being a strongly human microbiome-focused meeting (as opposed to other environmental microbiome or mixed host-associated and environmental microbiome meetings), by encouraging strong participation from trainees, and by encouraging sharing of unpublished information in an intimate format that enables deep and meaningful connections to be made. This meeting will be paired with the Keystone Symposia meeting, 'Microbiome Metabolism and Metabolites,' which will be strongly complementary to the program that is presented in this meeting.