Site Seeker, an interactive search tool for locating Critical Zone research field sites, is now online at www.czen.org/sites/site_seeker. Site Seeker is designed to facilitate collaboration and cooperation by allowing a user to quickly find sites with characteristics that may be of scientific interest. Currently Site Seeker contains field sites registered with CZEN.org and numerous other sites added by the CZEN web team. You can search these sites based on lithology, soil order, biome, land use, average precipitation and temperature, study time and research network affiliation. Currently most sites are located in the United States, but the goal is to add sites from around the world.