  For a simplicial complex $\Delta$, we introduce a simplicial complex attached
to $\Delta$, called the expansion of $\Delta$, which is a natural
generalization of the notion of expansion in graph theory. We are interested in
knowing how the properties of a simplicial complex and its Stanley-Reisner ring
relate to those of its expansions. It is shown that taking expansion preserves
vertex decomposable and shellable properties and in some cases
Cohen-Macaulayness. Also it is proved that some homological invariants of
Stanley-Reisner ring of a simplicial complex relate to those invariants in the
Stanley-Reisner ring of its expansions.
