Many copper-oxide-based superconducting compounds have been synthesized in recent years-currently more than 30 families are known, with superconducting transition temperatures up to 133 K. The structures of the various families are described, including La2CuO4, YBa2Cu3O7, single-layer superconductors, double-layer superconductors, and infinite layer materials (e.g., CaCuO2, as in the Figure).