Despite covering only 0.8% of the Earth's surface, freshwater biodiversity accounts for 9.5% of all described species. Aquatic macroinvertebrates, and in particular aquatic insects, are one of the most diverse faunal groups of fluvial ecosystems. Macroinvertebates are benthic invertebrates measuring more than 0.25 mm in size with a wide variety of biological and ecological traits, including different feeding types. Therefore, they constitute key elements of ecosystem functioning and provide significant ecosystem services. Among the taxonomic groups, there are representatives from Porifera, Cnidaria, Platyhelminthes, Mollusca, Annelida, Arachnida, Crustacea, and more than seven different orders of Insecta. A mixture of historical and ecological factors acting at different scales controls the diversity patterns of aquatic macroinvertebrates. However, dispersal characteristics and landscape dispersal limitations are also important. These organisms have been widely used as indicators of global change. In particular, many different biological indexes based on macroinvertebrates are being applied in different countries around the world to assess water quality. In addition, they are also good surrogates of climate change given their strong relationship with hydrological conditions, the dependency of their life cycles on temperature, and the high number of endemic and cold-stenothermic species. Forecasts of aquatic macroinvertebrate diversity and distribution are not very promising. Their most suitable habitats will be largely reduced in the near future and many species have a high risk of becoming extinct, which makes the implementation of conservation and management measures imperative.