Trichoptera – or caddisflies – are a highly diverse group of aquatic insects, their larvae inhabiting any type of fresh and slightly brackish waters. They play an important role in the trophic dynamics of both running and standing waters, and due to their high diversity, they are important indicators of environmental quality. The present book is the first comprehensive key to larvae of the Trichoptera species inhabiting northern Europe, taking its offset in Finland and adjacent countries. Recent barcoding techniques, using nuclei acid sequence analyses on mitochondrial DNA, have provided an enormous breakthrough in the present work, permitting a safer and easier association of adults with their larvae, several being hitherto unknown to science. The key presents essential morphological characters of the species with hundreds of detailed drawings and photos. With Trichoptera Larvae of Finland the authors intend to make the biodiversity and fascinating life of Trichoptera larvae available to anyone – professionals as well as amateurs – with interests in fresh and brackish waters.