Microorganisms play a central role in biogeochemical processes from decomposition to nitrogen transformations and therefore are central to our understanding of how ecosystems will respond in a changing world. There is growing interest in the functional role of microbes not only in natural ecosystems, but also in humans and in engineered systems. However, despite their functional importance, microbes are often ignored in studies of how biodiversity relates to ecosystem processes. The reasons for this oversight are at least two fold. First, microbial diversity is often assumed to be so high that any changes its diversity (composition and/or richness) are likely to be functionally irrelevant. Second, manipulating microbial communities in a realistic manner presents an enormous challenge because of their small size, high diversity, and difficulty to culture. At the same time, the ease of new sequencing methodologies have led to a glut of microbial community data, but interpretation of these data, and what they mean for functional processes, lags far behind. The goal of the session will be to share new approaches for investigating the relationship between microbial diversity/composition and functional processes while highlighting recent results in this area. Some of these studies use innovate approaches to manipulate microbial diversity in the lab, greenhouse, and field; in this way they can disentangle the effect of the community from other biotic and abiotic factors. Others use new statistical or conceptual models for better interpretation of community sequencing data. Still others take advantage of new molecular techniques that target specific microbial traits related to functioning.