We investigate shadowing effects in deep-inelastic scattering from nuclei at small values $x<0.1$ of the Bjorken variable. Unifying aspects of generalized vector meson dominance and color transparency we first develop a model for deep-inelastic scattering from free nucleons at small $x$. In application to nuclear targets we find that the coherent interaction of quark-antiquark fluctuations with nucleons in a nucleus leads to the observed shadowing at $x<0.1$. We compare our results with most of the recent data for a large variety of nuclei and examine in particular the $Q^2$ dependence of the shadowing effect. While the coherent interaction of low mass vector mesons causes a major part of the shadowing observed in the $Q^2$ range of current experiments, the coherent scattering of continuum quark-antiquark pairs is also important and guarantees a very weak overall $Q^2$ dependence of the effect. We also discuss shadowing in deuterium and its implications for the quark flavor structure of nucleons. Finally we comment on shadowing effects in high-energy photon-nucleus reactions with real photons.

26 pages, LaTeX, 16 PostScript figures available from http://www.physik.uni-regensburg.de/~c4080/prw/