  I review some of the experimental evidence and theoretical arguments that
suggest that pseudogap matter is a new form of matter that coexists with
coherent electron matter in the normal state and with superconducting matter
below the superconducting transition temperature. I describe work in progress
on a phenomenological two-fluid description of the evolution of pseudogap
behavior that offers an explanation for the unexpectedly simple scaling
behavior for the uniform magnetic susceptibility found in the underdoped
cuprates and use this to propose a physical picture of the underdoped cuprates
and to estimate the fraction of quasiparticles that become superconducting in
underdoped superconductors.
