  I describe recent theoretical and experimental progress in understanding the
physical properties of the two dimensional nearly antiferromagnetic Fermi
liquids (NAFL's) found in the normal state of the cuprate superconductors. In
such NAFL's, the magnetic interaction between planar quasiparticles is strong
and peaked at or near the commensurate wave vector, $Q \equiv (\pi,\pi)$. For
the optimally doped and underdoped systems, the resulting strong
antiferromagnetic correlations produce three distinct magnetic phases in the
normal state: mean field above $T_{cr}$, pseudoscaling between $T_{cr}$ and
$T_*$, and pseudogap below $T_*$. I present arguments which suggest that the
physical origin of the pseudogap found in the quasiparticle spectrum below
$T_{cr}$ is the formation of a precursor to a spin-density-wave-state, describe
the calculations based on this scenario of the dynamical spin susceptibility,
Fermi surface evolution, transport, and Hall effect, and summarize the
experimental evidence in its support.
