The stoichiometric RuO2(110) surface is terminated by bridge-coordinated oxygen atoms (O-beta) and by coordinatively unsaturated Ru (Ru-cus) atoms. Exposure to gaseous O-2 leads to the formation of two additional surface species: a molecularly chemisorbed state (O-delta) bridging two neighboring Ru-cus atoms and weakly held O atoms (O-gamma) in terminal position above the Ru-cus atoms. Characterization of the energetics and kinetics as well as structural, vibrational, and electronic properties is achieved by combined application of experimental (low-energy electron diffraction, high-resolution electron loss spectroscopy, thermal desorption spectroscopy) and theoretical (density functional theory) methods. The interplay between the different oxygen species accounts for the high sticking coefficient for dissociative adsorption as well as for the continuous restoration of the surface structure in the course of catalytic oxidation reactions.