Ecologists, particularly microbial ecologists, are faced with several grand scientific challenges in the 21^st century. Most of our planet's biodiversity remains unknown, especially microbial diversity. The mechanisms and processes shaping biodiversity are even more poorly understood. How different dimensions of biodiversity determining functional processes at the ecosystem level remain elusive. The response of ecological communities to global changes is not well understood. Another challenge is information scaling, how different organisms interact to yield the total functionality and stability of an ecosystem across different spatial, temporal, taxonomic, and organizational scales. The answers require and deserve continental- and global-scale investigation. Quite a few large-scale microbiome researches have been implemented and some ambitious plans are fermenting or just initiated, accumulating valuable data and new knowledge. In this session, we will present some key findings of current large-scale microbiome researches on several aspects, including discoveries and estimation of microbial biodiversity, biogeographic patterns and scale dependence, drivers and mechanisms underlying metacommunity patterns and local community assembly, etc. Besides, we would also like to discuss the challenges and share the experience in large-scale microbiome researches, including representativeness and comparability issues, organization strategy, the best practice from sampling to sequencing, data integration and management, national and international collaboration and coordination, etc.