  Back in the mid eighties, a new branch of investigation which was related to
the interaction of eta mesons with nuclei came into existence. It started with
the theoretical prediction of possible exotic states of eta mesons and nuclei
bound by the strong interaction and later developed into an extensive
experimental program to search for such unstable states as well as understand
the underlying interaction via eta meson producing reactions. The vast
literature of experimental as well as theoretical works which studied various
aspects of eta producing reactions such as the $\pi ^+$ $n$ $\to \eta p$, $p d
\to ^3$He $\eta$, $p \,^6$Li $\to ^7$Be $\eta$ and $\gamma ^3$He $\to \eta$ X,
to name a few, had but one objective in mind: to understand the eta - nucleon
($\eta N$) and hence the $\eta$-nucleus interaction which could explain the
production data and confirm the existence of some $\eta$-mesic nuclei. In spite
of these efforts, there remain uncertainties in the knowledge of the $\eta N$
and hence the $\eta$-nucleus interaction. The present review is hence an
attempt to bind together the findings in these works and draw some global and
specific conclusions which can be useful for future explorations.

Nuclear Theory