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.