Nematodes are the most abundant multicellular organisms on this planet and yet our knowledge of them is still very limited. They occur as parasites or free-living in virtually every environment, ranging from terrestrial soils, to sediments in fresh-, brackish-, and marine waters, down to the deepest trenches in the oceans. Free-living nematodes constitute a major part of the so called meiofauna, a group of different animal phyla with a size between 32 µm and 500 µm, which inhabits the interstitial space between the sand grains. In deep-sea sediments, more than 95% of all meiofauna organisms are free-living nematodes, with abundances ranging from 1mio. to 12mio. individuals per square meter. They express different feeding types, ranging from selective microbial feeders to predators and play a big role in nutrient recycling. But in one way or the other are all feeding-types reliant on food input from the water column above, whose composition is changing with changing environmental conditions in surface waters. Therefore, studying nematode diversity can be a way of monitoring surface/deep-sea relations and also effects of climate change in the deep ocean. The annual meiofauna sampling in the long-term ecological research deep-sea observatory HAUSGARTEN, which has been established by the Alfred-Wegener-Institute in the marginal ice zone of the Fram Strait more than 20 years ago, provides the world’s longest time series on deep-sea meiofauna, allowing for a comprehensive investigation of the deep-sea nematode community with abundance- and functional-based biodiversity analyses over spatial and temporal scales.