The aqueous solution behavior of An(III) (An = Am or Cm) in the presence of EDTA(4-) (ethylenediamine tetraacetate), CO32- (carbonate), and OH- (hydroxide) ligands has been probed in aqueous nitrate solution (various concentrations) at room temperature by UV-vis absorption and luminescence spectroscopies (Cm systems analyzed using UV-vis only). Ternary complexes have been shown to exist, including [An(EDTA)(CO3)](3-)((aq)), (where An = Am-III or Cm-III), which form over the pH range 8 to 11. It is likely that carbonate anions and water molecules are in dynamic exchange for complexation to the [An(EDTA)]-((aq)) species. The carbonate ion is expected to bind as a bidentate ligand and replaces two coordinated water molecules in the [An(EDTA)]-((aq)) complex. In a 1:1 Am-III/EDTA(4-) binary system, luminescence spectroscopy shows that the number of coordinated water molecules (N-H2O) decreases from similar to 8 to similar to 3 as pH is increased from approximately 1 to 10. This is likely to represent the formation of the [Am(EDTA)(H2O)(3)](-) species as pH is raised. For a 1:1:1 Am-III/EDTA(4-)/CO32- ternary system, the N-H2O to the [Am(EDTA)](-)((aq)) species over the pH range 8 to 11 falls between 2 and 3 (cf. similar to 3 to similar to 4 in the binary system) indicating formation of the [An(EDTA)(CO3)](3-)((aq)) species. As pH is further increased from approximately 10 to 12 in both systems, there is a sharp decrease in N-H2O from similar to 3 to similar to 2 in the binary system and from to similar to 2 to similar to 1 in the ternary system. This is likely to correlate to the formation of hydrolyzed species (e.g., [Am(EDTA)(OH)](2-)((aq)) and/or Am(OH)(3(s))).