This study, commissioned by the German Umweltbundesamt, aims at quantifying, within ranges as small as possible, external costs from environmental impacts of aviation. Benefits of aviation are important too, but they are generally, in contrast to the negative impacts, well captured by the market. For the valuation of climatic impacts from aviation, both the damage cost and prevention cost approach is used, leading to a middle estimate of 30 per tonne of CO2 equivalent, with sensitivities of 10 and en 50 per tonne. As contrails have a relatively large climatic impact and their formation can quite accurately be predicted, the climatic impact is differentiated for situa-tions with and without contrail formation. For this analysis the most important assumption is hat contrails are formed during 10% of flight kilometres. For the valuation of regional and local impacts, the damage cost approach has been followed. Avoidance or adaptation costs (e.g. costs of zoning around airports) have been included in the damage cost assessment. For aircraft flying at distances up to a few hundred kilometres, external costs related to landing and take-off (LTO) impacts especially noise - are dominant in the total picture. For flights over about 1,000 km, external costs of climatic impacts exceed those of LTO impacts, also in case no contrails are formed. New technology has more impact on LTO related costs than on costs related to climatic impact. Contrail formation has a large influence on the climatic impact of aircraft, and thus on external costs related to this climatic impact. Based on a number of assumptions, a middle estimate is that the climatic impact of a contrailcausing aircraft km is, on average, about eight times as high as an aircraft km that does not lead to persistent contrails. Expressed as a share of ticket prices, external costs (without contrail impacts) vary from roughly 5% of ticket prices (long-haul flights, new technol-ogy, no contrail formation) to roughly a quarter of ticket prices for 200 km flights with average technology. These figures rise sharply when contrails are formed during part of the trip.