Cu(I) coordination by organoselenium compounds was recently reported as a mechanism for their prevention of copper-mediated DNA damage. To establish whether direct Se-Cu coordination may be involved in selenium antioxidant activity, Cu(I) coordination of the selenoamino acids methyl-Se-cysteine (MeSeCys) and selenomethionine (Se Met) was investigated. NMR results in D2O indicate that Cu(I) binds to the Se atom of both MeSeCys and Se Met as well as the carboxylic acid oxygen atom(s) or amine nitrogen atoms. X-ray absorption spectroscopy (XAS) and density functional theory (DFT) results confirm Se-Cu coordination, with the identification of a 2.4 angstrom Se-Cu vector in both the Se-and Cu-EXAFS data. XAS studies also show Cu(I) in an unusual three-coordinate environment with the additional two ligands arising from O/N (2.0 angstrom). DFT models of 1:1 Cu-selenoamino acid complexes suggest that both selenoamino acids coordinate Cu(I) through the selenium and amino groups, with the third ligand assumed to be water. These compounds represent the first structurally characterized copper(I) complexes with sulfur- or selenium-containing amino acids.