  The possibility of using the optimized $\delta$ expansion for studying medium
effects on hadronic properties in quark or nuclear matter is investigated. The
$\delta$ expansion is employed to study density effects with two commonly used
models in hadron and nuclear physics, the Nambu--Jona-Lasinio model for the
dynamical chiral symmetry breaking and the Walecka model for the equation of
state of nuclear matter. The results obtained with the $\delta$ expansion are
compared to those obtained with the traditional Hartree-Fock approximation.
Perspectives for using the $\delta$ expansion in other field theoretic models
in hadron and nuclear physics are discussed.
