  We investigate the effect of a finite volume on the critical behavior of the
theory of the strong interaction (QCD) by means of a quark-meson model for two
quark flavors. In particular, we analyze the effect of a finite volume on the
location of the critical point in the phase diagram existing in our model. In
our analysis, we take into account the effect of long-range fluctuations with
the aid of renormalization group techniques. We find that these quantum and
thermal fluctuations, absent in mean-field studies, play an import role for the
dynamics in a finite volume. We show that the critical point is shifted towards
smaller temperatures and larger values of the quark chemical potential if the
volume size is decreased. This behavior persists for antiperiodic as well as
periodic boundary conditions for the quark fields as used in many lattice QCD
simulations.
