It has only recently been recognized that biological soil crusts (BSC) are a critical component of dryland ecosystems, contributing to the diversity, functionality and nutrient cycling of these regions worldwide. Formed by cyanobacteria, algae, lichens, fungi and bacteria in varying proportions, BSC grow within the uppermost millimeters of the soil, fulfilling a variety of ecosystem services. With their filaments BSC organisms glue together soil particles, thus effectively preventing erosion by both wind and water. BSC organisms in general and nitrogen-fixing cyanobacteria in particular, add nutrients to nutrient-poor desert soils, thus promoting the establishment and growth of vascular plants. Their relevance and impact on global carbon and nitrogen cycles is just starting to be considered. During the last decade, studies on BSC have intensified and diversified, creating a unique and growing research community. As many of these topics are essential to understand the structure and function of dryland ecosystems, this research should be presented to the larger scientific community. The session is designed to provide an overall synthesis, covering all major fields of current BSC research at high scientific quality.