Dictyostelids (Amoebozoa) are a group of social amoebae consisting of approximately 150 species, which are found in terrestrial habitats worldwide. They are divided into eight major clades based on molecular phylogeny, and within these clades are many species complexes. Some species are seemingly cosmopolitan in distribution, while others are geographically restricted. In this thesis dictyostelids were recovered from high latitude habitats (soils in Sweden and Iceland) as well as from the soles of shoes. Morphological characters and DNA sequence analyses were used to identify isolates that were recovered and delimit new species, as well as to investigate the monophyly of Dictyostelium aureostipes. Nine species were reported from Northern Sweden and four from Iceland. Among the isolates recorded in Sweden were two new species, described as D. barbibulus and Polysphondylium fuscans. P. fuscans was among the four species recovered from footwear, contributing evidence for anthropogenic transport of dictyostelids. Ecological patterns were assessed using linear regression and generalized linear models. The ecological analyses of dictyostelids recovered from Iceland indicate that these organisms are most frequently found in soils of near-neutral pH, but also exhibit a species richness peak in moderately acidic soils. These analyses indicate that in Iceland dictyostelid species richness decreases with altitude, and in the northern hemisphere the species richness increases with decreasing latitude. A three-region analysis of the D. aureostipes species complex indicated that this species is in fact made up of at least five phylogenetically distinct clades, and in light of this the group is in need of taxonomic revision. These results indicate that the dictyostelid species richness is higher than previously known, especially in high-latitude regions, and that even seemingly well-defined species may harbour cryptic diversity. Presently, species ranges may be expanding via anthropogenic dispersal but despite this, the dictyostelids are found to exhibit biogeographic trends well known from macroorganisms, such as a latitudinal gradient of species richness.