Biological soil crusts (biocrusts) are soil surface, primary producing communities of autotrophs � including cyanobacteria, mosses, and lichens connected with a diverse microbiome of heterotrophic prokaryotes, and fungi. They predate vascular plants but remain globally widespread, mostly where soils are exposed to sunlight through open canopies (dryland, alpine, high latitude, or disturbed habitats). In these ecosystems, biocrusts contribute to local biodiversity and play fundamental roles in ecosystem function: stabilizing soils, fixing C and N, and regulating hydrology. Despite these key roles, we have only a disconnected - primarily local instead of global - understanding of biocrust distribution, function, and response to global change. To bring global scale insight to biocrust research and test fundamental ecological theory on a widespread but understudied community, we propose CrustNet: a networked, distributed study of biocrust ecology. With CrustNet, we will address: (1) The determinants of the global scale functional biodiversity of biocrusts (2) determinants of the variability and shape of the biodiversity-function (BEF) relationship among ecosystems, and (3) Effects of biocrust functional biodiversity on resistance and resilience to physical disturbance and climate change. A tiered research protocol, including low-cost observational studies and manipulative experiments, will be deployed at many international sites. We have identified 70 research groups interested in participating, working in 26 countries on 7 continents. Protocols have been field-tested. Our objective is to coordinate this international effort, provide crucial analytical capacity, and make global-scale inferences about the causes and consequences of biocrust biodiversity.