  Recent progress in Lorentz-covariant quantum field theories of the nuclear
many-body problem (quantum hadrodynamics or QHD) is discussed. The effective
field theory studied here contains nucleons, pions, isoscalar scalar (\sigma)
and vector (\omega) fields, and isovector vector (\rho) fields. The theory
exhibits a nonlinear realization of spontaneously broken SU(2) \times SU(2)
chiral symmetry and has three desirable features: it uses the same degrees of
freedom to describe the nuclear currents and the strong-interaction dynamics,
it satisfies the symmetries of the underlying theory of QCD, and its parameters
can be calibrated using strong-interaction phenomena, like hadron scattering or
the empirical properties of finite nuclei. Moreover, it has recently been
verified that for normal nuclear systems, it is possible to expand the
effective lagrangian systematically in powers of the meson fields (and their
derivatives) and to truncate the expansion reliably after the first few orders.
Using a mean-field version of the energy functional, accurate quantitative
results are obtained for the bulk and single-particle properties of medium- and
heavy-mass nuclei. The importance of modern perspectives in effective field
theory and density functional theory for understanding these successes of QHD
is emphasized. The inclusion of hadronic electromagnetic structure and of
nonanalytic terms in the energy functional is also considered briefly.
Weak-interaction currents are also studied in this QHD framework. Expressions
for the axial-vector current, evaluated through the first few orders in the
field expansion, satisfy both PCAC and the Goldberger--Treiman relation.
Moreover, the corresponding vector and axial-vector charges satisfy the
familiar chiral charge algebra to all orders in the pion field.
