Permafrost environments within the Siberian Arctic are natural sources of the climate relevant trace gas methane. In order to improve our understanding of the present and future carbon dynamics in high latitudes, we studied the methane concentration, the quantity and quality of organic matter, and the activity and biomass of the methanogenic community in terrestrial and submarine permafrost deposits. For these investigations permafrost cores of Holocene and Pleistocene ages were drilled in the Laptev Sea region. The organic carbon of the permafrost sediments varied between 0.6% and 4.9% and was characterized by an increasing humification index with permafrost depth. A high methane concentration was found in distinct horizons of the deposits, which correlates well with the methanogenic activity and archaeal biomass (expressed as PLEL concentration). Even the incubation of core material at 3 and 6°C with and without substrates showed a significant methane production (range: 0.040.78 nmol CH4 h 1 g 1). The results indicated that the methane in Holocene and Pleistocene permafrost deposits of the Laptev Sea region originated from modern methanogenesis by cold-adapted methanogenic archaea. Owing to the subzero experiments and the in situ temperatures of permafrost sediments, we can conclude that the methanogenic community is dominated by psychrotolerant or even psychrophilic microorganisms. Despite this adaptation to cold environments, we show that a slight increase of the temperature can lead to a substantial increase of methanogenic activity. In case of permafrost degradation, this would lead to an extensive expansion of the methane deposits with their subsequent impacts on total methane emission. A future in-depth characterization of the metabolism of these cold-adapted methanogens will reveal biotic and abiotic factors, which influence the methanogenic activity of these organisms.Furthermore, the results further show that methane in permafrost, which originates from modern methanogenesis, represents contribution thus so far not considered to the global methane budget. The methane is released to the atmosphere by permafrost degradation in form of thermokarst or coastal erosion processes, which is an ongoing process in Arctic regions. Although the change of permafrost by global warming is examined in the framework of different international projects, these investigations should be linked more strongly with microbiological process studies and biodiversity research. Thus, a contribution could be made to understand the role of permafrost in the global system and possible feedbacks by material fluxes and greenhouse gas emissions.