Since its discovery in the earth’s atmosphere in 1938, N2O sources and sinks have been a puzzle. N2O has now been identified as produced by anaerobic bacteria’s in soils which are sufficiently acid. The influence of agriculture is still to be determined as the nitrogen cycle is broken by both the addition of inorganic fertilizers and the simultaneous oxygenation of soils by mechanized agriculture. The situation was even complicated recently by the discovery of an abiotic N2O production in the Antarctic brines (Samarkin et al. 2010). In the last 10 years, a global increase has been observed and N2O is considered as a greenhouse gas in the current IPCC report. It is destroyed by direct oxidation by oxygen atoms in the stratosphere where it is also sensitive to photodissociation. The observation of N2O from space is possible as several of its bands are in infrared atmospheric windows, especially the strong 7.8, 4.5 and the weaker 3.7μm bands. Terrestrial N2O would be both a by-product of a subterranean biosphere and of the current agricultural practices. Its oxidation produces also tropospheric nitric oxide in the unpolluted troposphere, in limited quantities, No also plays an important role for biological processes.