Quasiparticles and phase fluctuations in high Tc superconductors

We argue based on theoretical considerations and analysis of experimental d ata that quasiparticle excitations near the nodes determine the low tempera ture properties in the superconducting state of cuprates. Quantum effects o f phase fluctuations are shown to be quantitatively important, but thermal effects are small for T << T-c. An anisotropic superfluid Fermi liquid phen omenology is presented for the effect of quasiparticle interactions on the temperature and doping dependence of the low T penetration depth.