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The results from investigations on oribatid mites of the Galgpagos archipelago during 10 years are presented. Samples were taken on all larger and most smaller islands of the archipelago, as well as in all vegetation zones and some special habitats such as grass or cactus litter and fumaroles. A total of 202 oribatid species belonging to 64 families were encountered; among them 81 species are new to science. The Oribatida occur from the littoral zone to the summit of the volcanoes. Diversity and abundance increases from the arid to the moister zones at higher elevations. Most species prefer moist habitats at medium to higher elevations of the islands, in some parts reaching remarkably high abundances (in the Scalesia zone of Santa Cruz approximately 18 000 individuals m(-2)). The species richness of an island depends on the altitude and number of available habitats rather than the area of the island. Many oribatid species on the Galapagos Islands have a wide biogeographical distribution. The majority originate from the Central and South American mainland, but several Pacific and even Holarctic elements were also found. In comparison with the species composition of the adjacent mainland, the oribatid mite fauna of the Galapagos Islands can be regarded as disharmonic. Sea surface transportation has been proved at least between the islands, which also applies to oribatid species living at higher elevations. Long distance dispersal can be assumed to be mainly hydrochorous. The oribatid fauna of the littoral and arid vegetation zones is presented in detail. Some species even inhabit such extreme habitats as warm fern litter in fumaroles or hot volcanic soils. Others were mainly found in or near a,ori cultural areas, suggesting human introduction. Striking distribution patterns within the archipelago are discussed. The distribution of endemic forms in the genera Aeroppia, Scapheremaeus, Schleoribates and Cultrobates indicates both speciation on different islands, as well as speciation on the same island by occupying different habitats. Exp Appl Acarol 22: 373-409 (C) 1998 Chapman & Hall Ltd.