  We discuss a dramatic change brought into the pQCD description of hard
processes in a nuclear environment by a large thickness of heavy nuclei. It
breaks the familiar linear $k_{\perp}$-factorization which must be replaced by
a new concept of the nonlinear $k_{\perp}$-factorization introduced in
\cite{Nonlinear}.We demonstrate the salient features of nonlinear
$k_{\perp}$-factorization on several examples from hard dijet production in DIS
off heavy nuclei to single-jet to dijet production in hadron-nucleus collisions
>. We also comment briefly on the non-linear BFKL evolution for gluon density
of nuclei.
