Habitat degradation is a primary driver of biodiversity loss, with effects on ecosystem functioning. In stream ecosystems, leaf litter decomposition plays a fundamental role in energy and nutrient cycling, being influenced by leaf litter quality, microbial and macroinvertebrate consumers, and environmental conditions. Land use changes (such as deforestation and the expansion of agricultural, urban, or plantation landscapes), alter stream habitats and can significantly modify decomposition rates and dynamics. However, large-scale assessments of these impacts remain limited. By comparing decomposition rates across several regions of SW Europe encompassing a strong climatic gradient, we assessed the influence of land use type (forest, urban, agriculture and plantation), climate and leaf litter quality on microbial and macroinvertebrate-mediated leaf litter decomposition. We used several leaf litter types, including local species and standardized species for comparison across sites. The study used a subset of sites from the LandComp study, one of the very few global-scale initiatives that provide critical insights into the patterns and drivers of stream ecosystem functioning.