This is the first part of a multi-volume monograph dealing with about 400 species of springtails (Collembola) which are known to occur in the Nordic countries, including the Arctic Islands. Volume 1 contains illustrated identification keys and full descriptions of 161 species of the section Poduromorpha. The geographical distribution and the preferred natural habitats of the species are summarized. New morphological concepts in species diagnostics are introduced, in particular concerning mouthparts' morphology which greatly aids in precise identification of the many difficult species of the family Onychiuridae. The Collembola of Fennoscandia and Denmark: Part 1: Poduromorpha should be a useful guide to everyone working with springtail identification in northern Europe, as will the introduction of new diagnostic characters to any Collembola taxonomist.