Iridium is important for developing ultrahigh‐temperature oxidation‐resistant coatings, in addition to its role in catalysis and potential as an effective oxygen diffusion barrier for multilayered coatings. We present an ab initio density‐functional study of aluminum adsorption on Ir (111) at high symmetry sites, i.e., the fcc‐, hcp‐hollow, top, and bridge sites. The atomic geometry, average binding energy, work function, and surface dipole moment at a coverage of 0.25–1 monolayer are calculated. A favorable structure is found to be Al at the threefold hcp‐hollow site, with a corresponding binding energy of 4.46 eV. We compare the electronic properties of the two lowest energy structures, i.e., the threefold hollow sites, and discuss the nature of the Al‐Ir bond and binding site preference. A large hybridization of the Al‐3s, 3p, and Ir‐5d states is observed near the Fermi level, forming intermetallic bonds. This results in significant electron transfer from the Al atoms to the Ir (111) substrate, inducing an outward pointing surface dipole moment and a large decrease of 1.69 eV in the work function for Al at the hcp‐hollow site. Adsorption at this site results in a lower density‐of‐states compared to the fcc‐hollow site, as well as greater hybridization in the bonding states.Iridium is important for developing ultrahigh‐temperature oxidation‐resistant coatings, in addition to its role in catalysis and potential as an effective oxygen diffusion barrier for multilayered coatings. We present an ab initio density‐functional study of aluminum adsorption on Ir (111) at high symmetry sites, i.e., the fcc‐, hcp‐hollow, top, and bridge sites. The atomic geometry, average binding energy, work function, and surface dipole moment at a coverage of 0.25–1 monolayer are calculated. A favorable structure is found to be Al at the threefold hcp‐hollow site, with a corresponding binding energy of 4.46 eV. We compare the electronic properties of the two lowest energy structures, i.e., the threefold hollow sites, and discuss the nature of the Al‐Ir bond and binding site preference. A large hybridization of the Al‐3s, 3p, and Ir‐5d states is observed near the Fermi level, forming intermetallic bonds. This results in significant electron transfer from the Al atoms to the Ir (111) substrate, inducin...