  The vast majority of the literature dealing with quantum dynamics is
concerned with linear evolution of the wave function or the density matrix. A
complete dynamical description requires a full understanding of the evolution
of measured quantum systems, necessary to explain actual experimental results.
The dynamics of such systems is intrinsically nonlinear even at the level of
distribution functions, both classically as well as quantum mechanically. Aside
from being physically more complete, this treatment reveals the existence of
dynamical regimes, such as chaos, that have no counterpart in the linear case.
Here, we present a short introductory review of some of these aspects, with a
few illustrative results and examples.
