This grant supports a team led Noah Fierer, associate professor at the University of Colorado; Rob Dunn, associate professor at North Carolina State; and Shelly Miller, an environmental engineer and associate professor at the University of Colorado to characterize the diversity of microbial communities in homes throughout the United States. Tapping a network of more than 6,500 volunteers across the U.S., Fierer and his team will collect information on volunteer homes and distribute "home sampling kits" which direct volunteers to collect swabs of the microbial populations living in four locations in the home: the outer door frame above the entrance to the residence, a door frame above an interior door, a kitchen countertop where food is prepared, and a pillowcase on a bed. As a complement to the larger study, the team will conduct a detailed study of the microbial populations in 50 homes in the Boulder, Colorado region, collecting microbial samples on multiple occasions and making a variety of building measurement, including humidity, temperature, and levels of carbon monoxide and carbon dioxide. Taken together, the two studies will permit the construction of what promises to be the most complete picture of how residential microbial communities differ across the United States and will provide a huge dataset that can be used to generate and test hypotheses on what factors drive the compositional diversity of microbial communities in the built environment.