  We review a recently developed method, based on a pseudoparticle
representation of correlated electrons, to describe both Fermi liquid and
non-Fermi liquid behavior in quantum impurity systems. The role of the
projection onto the physical Hilbert space and the impossibility of slave boson
condensation are discussed. By summing the leading coherent spin and charge
fluctuation processes in a fully self-consistent and gauge invariant way one
obtains the correct infrared behavior of the pseudoparticles. The temperature
dependence of the spin susceptibility for the single channel and two-channel
Anderson models is calculated and found to agree well with exact results.
