Control of structure and order in oxides is essential for the design of new superconducting cuprates. The intergrowth of perovskite and rock salt layers, as found in bismuth, thallium and, very recently, the recordbreaking mercury cuprates. is just one way to induce bidimensionality. Defect ''all perovskite'' oxides, such as Ln(2)Ba(2)Cu(2)Ti(2)O(11) (Ln = La, Nd, Eu) are discussed as examples of a crystal-chemical approach to the induction of bidimensionality and order in mixed perovskite oxides of copper.