We develop a general theory of fermion liquids in spatial dimensions greater than one. The principal method, bosonization, is applied to the cases of short and long range longitudinal interactions, and to transverse gauge interactions. All the correlation functions of the system may be obtained with the use of a generating functional. Short-range and Coulomb interactions do not destroy the Landau Fermi fixed point. Novel fixed points are found, however, in the cases of a super-long range longitudinal interaction in two dimensions and transverse gauge interactions in two and three spatial dimensions. We consider in some detail the 2+1-dimensional problem of a Chern-Simons gauge action combined with a longitudinal two-body interaction $V({\bf q}) \propto |{\bf q}|^{y-1}$ which controls the density, and hence gauge, fluctuations. For $y < 0$ we find that the gauge interaction is irrelevant and the Landau fixed point is stable, while for $y > 0$ the interaction is relevant and the fixed point cannot be accessed by bosonization. Of special importance is the case $y = 0$ (Coulomb interaction) which describes the Halperin-Lee-Read theory of the half-filled Landau level. We obtain the full quasiparticle propagator which is of a marginal Fermi liquid form. Using Ward Identities, we show that neither the inclusion of nonlinear terms in the fermion dispersion, nor vertex corrections, alters our results: the fixed point is accessible by bosonization. As the two-point fermion Green's function is not gauge invariant, we also investigate the gauge-invariant density response function. Near momentum $Q = 2 k_F$, in addition to the Kohn anomaly we find singular behavior. In Appendices we present a numerical calculation of the spectral function for a Fermi liquid with Landau parameter $f_0 \neq 0$. We also show how Kohn's theorem is

Minor corrections and clarifications, and additional references. 30 pages, RevTex 3.0, 3 figures in uuencoded postscript files.