  This article is based on a series of lectures given at ELAF 93 on the
description of low-energy hadronic systems {\it in and out} of hadronic medium.
The focus is put on identifying, with the help of a Cheshire Cat philosophy,
the effective degrees of freedom relevant for the strong interactions from a
certain number of generic symmetry properties of QCD. The matters treated are
the ground-state and excited-state properties of light- and heavy-quark baryons
and applications to nuclei and nuclear matter under normal as well as extreme
conditions.
