The present status of Josephson effect and tunnel effect of high Tc oxide superconductors is reviewed. In the beginning, the concepts for Josephson and tunnel effects are introduced. With respect to the Josephson effect, the properties of grain boundary junctions are discussed in detail, especially based on the observed current-voltage characteristics and the quantum interference effect. As for the tunnel experiment, a variety of data are presented and discussed in connection with the proposed theoretical models. Finally, the problems on the formation of an ideal Josephson tunnel junction are discussed.
