Results of our NMR measurements of highT c superconductors are reviewed. From systematic measurements of NQR frequency, Knight shift, nuclear spin lattice relaxation rate and nuclear transverse relaxation rate over a wide hole concentration range from light to heavy doped compounds together with the impurity and pressure effect, following results are concluded. The numbers of the holes at the respective sites of Cu and O site in the CuO2 plane govern the several physical properties of the system. There are optimum values of these hole numbers to produce highestT c . The superconducting properties are well explained consistently by thed-wave pairing model.T c is found to be correlated intimately with the antiferromagnetic spin fluctuation parameters that governs the nuclear relaxation. The mechanism for the superconductivity is magnetic in origin.