The course will provide an introduction to microbial diversity in natural environments, with a particular focus on bacteria, archaea and fungi. Students will learn about the central role of microorganisms in biogeochemical cycles in soils, oceans, and freshwater systems. Relationships between microbes and higher organisms (e.g. plant-fungi symbioses) will also be discussed. There will be an overview of methods for studying microbial community diversity and function - from culture-based methods to molecular markers (e.g. sequencing of DNA/RNA). The focus will be on linking specific scientific questions to particular techniques. Alongside this there will be a short introduction to bioinformatics for microbiome sequence data. Finally, we will conduct discussions of recent scientific literature in microbial ecology, to sharpen students' skills in critical reading.