  The threshold region for processes of hadronic and nuclear interactions is
very interesting for a theoretical as well as an experimental point of view. In
this region one can apply different physical methods, starting from classical
current algebra methods - for processes invloving soft pions, through effective
Lagrangian approaches - or perturbative chiral symmetry theory (ChPT). The
essential simplification of the spin structure of matrix elements for threshold
regime results in better understanding of the underlying mechanisms and allows
the analysis of polarization phenomena. A dedicated formalism is developed here
for a wide class of processes including even such complicated processes as
production of pseudoscalar and vector mesons in nucleon-nucleon collisions.
Many interesting physical problems are discussed: hidden strangeness of
nucleons and OZI-violation, $\eta N$ -and $\omega N$ interactions in S-state,
the determination of P-parity of strange particles. Special attention is
devoted to the analysis of the spin structure and polarization phenomena for
nuclear processes with light nuclei which have important applications in
fundamental astrophysics and in nuclear fusion.
