One of the objectives of Sloan's Indoor Environment program is to support targets of opportunity that will help to advance research and knowledge about the indoor microbial environment. Funds from this grant support research on the indoor microbial environment by a team of scientists at the University of California, Berkeley. Their research plan has three objectives: 1) to investigate the processes of microbial community assembly in the indoor environment; 2) to obtain an understanding of the relationship between building design, external climate, and interior microbial community; and 3) to improve instrumentation to measure volatile, organic compounds derived from microbes, microbial toxins, and allergens in indoor air. The Berkeley team's project complements existing Foundation grants supporting the Biology and Built Environment Center at the University of Oregon, which is developing a predictive science of the built environment microbiome through partnerships between architects and biologists; a major ongoing research project to catalog the indoor microbial world at the University of Colorado at Boulder; a project to study New York City air and to develop a single cell genomics pipeline at the J. Craig Venter Institute, and efforts by the Marine Biological Laboratory at Woods Hole to examine the rare biosphere in drinking water.