A workshop on Gut Microbiome: Markers of Human Health, Drug Efficacy and Xenobiotic Toxicity will be held on Monday and Tuesday, June 25–26, 2018, in Alexandria, Virginia. The gut microbiome is believed to play an important role in human health in areas as diverse as brain function and the immune system. Exploring host-microbiome interactions will provide a mechanistic understanding and enable new insights in human disease (i.e., their diagnosis, prognosis, and treatment) and new perceptions of xenobiotic efficacy and/or toxicity. The goal of the workshop is to identify data gaps that can be addressed to help determine if alterations in the gut microbiome have an effect on human health. The workshop was organized by the Health and Environmental Sciences Institute (HESI) Microbiome Committee. For more information and to register, please visit the conference website. Registration closes on Wednesday, June 19.