Book excerpt: Watersaturated soil and sediment ecosystems (i.e. wetlands) are ecologically as well as economically important systems due to their high productivity, their nutrient (re)cycling capacities and their prominent contribution to global greenhouse gas emissions. Being on the transition between terrestrial and – aquatic ecosystems, wetlands are buffers for terrestrial run off thereby preventing eutrophication of inland as well as coastal waters. The close proximity of oxic-anoxic conditions, often created by wetland plant roots, facilitates the simultaneous activity of aerobic as well as anaerobic microbial communities. Input of nutrients and fast recycling due to active aerobes and anaerobes makes these systems highly productive and therefore attractive for humans as well as many other organisms. Wetlands globally are under high pressure due to anthropogenic activities as well as climate change. Changes of land-use as well as altered hydrology due to climate change will lead to disturbance and loss of these habitats. However, the diversity and functioning of microbial communities in wetlands systems in highly underexplored in comparison to soils and aquatic ecosystems. Given the importance of wetlands and their immediate threats combined with the lack of knowledge on the microbiology of these systems is the basis for this special issue, focusing on the current microbiological knowledge and gaps therein to be assessed in future wetland research. Papers (research papers, reviews, perspectives, opinion papers) are welcomed that focus on all aspects that regulate the functioning and community composition of microbes (i.e. bacteria, archaea, protozoa, fungi) in wetland ecosystems (peat, coastal as well as freshwater marshes, flood plains, rice paddies, littoral zones of lakes etc) from all geographic regions. Welcomed topics are physiology, ecology, functioning, biodiversity, biogeography of microbes involved in nutrient cycling (C, N, P, Fe, Mn), green house gas emissions as well as plant-microbe interactions. These studies can be multidisciplinary and cover topics from the molecular to the community level.