By means of density functional theory and experiments, surface chemical reactivity of single crystals of NbAs and TaAs Weyl semimetals is studied. Weyl semimetals exhibit outstanding reactivity toward simple molecules (oxygen, carbon monoxide, and water), with several active sites available for surface chemical reactions (adsorption, decomposition, formation of reaction products, recombination of decomposition fragments). When different chemical species are adsorbed on Weyl semimetals, strong lateral interactions between coadsorbed species occur, evidenced by CO‐promoted water decomposition at room temperature. The resulting OH groups react with CO to form HCOO, which is an intermediate species in water–gas shift reaction. These findings unambiguously demonstrate that Weyl semimetals could be effectively used in catalysis, whereas their employment in nanoelectronics or plasmonics is …