  In this report we show that vacuum is a nonlinear optical medium and we
discuss what are the optical phenomena that should exist in the framework of
the standard model of particle physics. We pay special attention to the low
energy limit. The predicted effects for photons of energy smaller than the
electron rest mass are of such a level that none has been observed
experimentally yet. Progresses in field sources and related techniques seem to
indicate that in few years vacuum nonlinear optics will be accessible to human
investigation.
