Abstract Ruthenium is the most active and stable promoter of platinum known for low-temperature fuel cell anode reactions such as the oxidation of methanol and CO. The mechanism of promotion by Ru, including bifunctional and ligand effects, is discussed in this selective review. Also examined are effects of surface structure, Ru distribution, and Ru oxidation state. For this purpose, some review of the mechanism of CO and methanol oxidation on Pt/Ru surfaces is provided. The review concentrates on pure Pt nanoparticles and bulk electrodes modified by deposition of Ru, although some discussion of Pt/Ru alloys and Pt-modified Ru electrodes is included in order to address and discuss all aspects of promotion by Ru.