Ligation of atomic gold(I) cation Au+ by various inorganic and organic ligands containing heteroatoms has been examined by experimental and theoretical means. The Au(Xe)(+) complex has been studied comprehensively by CCSD(T) calculations in order to provide a benchmark for a gold(I) cation affinity scale, The best theoretical estimate of the binding energy is D-0(Au+-Xe) = 30.1 kcal/mol. This value is used to relate calculated and experimentally bracketed binding energies of Au(L)(+) complexes with a relative gold(T) cation affinity scale for heteroatom ligands L, i.e., Xe < C6F6 < H2O < CO < H2S < CH3CN approximate to C2H4 approximate to NH3 approximate to CH3NC < CH3SCH3 < PH3. In comparison to other transition metal cations, the gold(I) cation is unique in that the binding energies to several ligands are exceptionally large. Further, the covalent character of the Au+-L bonds as well as charge transfer from the ligand to gold are significant. Finally, the gas-phase behavior of Au+ suggests some implications for possible new approaches to gold(I) chemistry in condensed matter.