Our recent results on the resistivity of the single layer cuprate superconductors, and the conditions determining Tc for a d-wave superconducting state in 2-dimensions are summarized. The resistivity found is quasi-linear in T and in quantitative accord with data. The phase diagram for superconductivity has a stretched- dome structure, with a peak Tc of a few hundred K, and a peak density determined by band parameters. The calculations are based on the t-J model in 2-dimension, and the extremely correlated Fermi liquid theory (ECFL) used is non-perturbative in character. In the talk we will go light on technical details, and highlight the physical ideas behind the calculations.