The in‐plane resistivity data, &rgr;∥(T), as a function of temperature for various Cu‐oxide superconductors have provided strong evidence for a Fermi‐liquid normal state and also important clues for understanding the mechanism responsible for high‐temperature superconductivity. A dominant quadratic temperature dependence of &rgr;∥(T) above Tcis observed in the electron‐ doped NdCeCuO system and several relatively low‐Tchole‐ doped cuprates. On the other hand, high TcCu oxides (Tc≳80 K) are always characterized by a linear temperature dependence of &rgr;∥(T). Within the framework of the BCS phonon‐mediated pairing, the closeness of a 2D van Hove singularity in the density of states to the Fermi level provides a basis for understanding the origin of high‐temperature superconductivity, the correlation between Tcand &rgr;∥(T), anomalous isotope effects and several other normal‐state and superconducting properties.