A basic understanding of the copper oxide high-Tc superconductors is reviewed. Crystal structures of the oxide superconductors are described in terms of their basic structures of Cu-O plane. Electric properties are closely related with the carrier concentration in the system, and a model for the electronic structures of the oxide superconductors is shown. The role of Cu-O plane is discussed for a design of a new layered copper oxide high-Tc superconductors by employing the block layer model.
