The crystalline structure of copper-oxygen compounds with copper atom in the oxidation states I, 11, and I11 is reviewed. A calculation is made of the electronic structure of the row of crystals with copper-oxygen bonding. It is shown that the covalence effects are essential for copper oxide compounds containing copper atoms in oxydation states Cur1 and CuIII. LUC-CNDO calculations of La,CuO, and YBa,Cu,O, (5 = 6,7) crystals are made. It is concluded that the higher copper valency is favourable for superconductivity.