We present the results of a study concerning the interaction of atomic oxygen (as released by decomposition of N2O ) with the clean Ge(001)2×1 surface at 300 K. Ellipsometry in the photon energy range of 1.5–4 eV, surface conductance measurements and Auger electron spectroscopy (AES) have been used to monitor this solid–gas reaction. Adsorption of N2O on the clean Ge(001) surface was found to terminate at monolayer coverage. As compared to the adsorption of molecular oxygen (O2), we observed in the joint density of states a splitting of the 1.8 eV peak into peaks at 1.7 and 2 eV plus an additional weak shoulder at 2.3 eV. Surface conductance measurements indicate that the adsorption process is dominated by the removal of filled surface states (dimer and dangling bond of the up atom). Atomic oxygen goes into a bridging position between top layer Ge atoms, in the initial stage first by decomposing at the Ge–Ge dimer bonds. The adsorption behavior of N2O at the Ge(001)2×1 surface is similar to that at the closely related Si(001)2×1 surface [Keim et al., Surf. Sci. 180, 565 (1987)]. Our results confirm the site specificity of the N2O molecule.