  The phenomena implied by the existence of quantum vacuum fluctuations,
grouped under the title of the Casimir effect, are reviewed, with emphasis on
new results discovered in the past four years. The Casimir force between
parallel plates is rederived as the strong-coupling limit of $\delta$-function
potential planes. The role of surface divergences is clarified. A summary of
effects relevant to measurements of the Casimir force between real materials is
given, starting from a geometrical optics derivation of the Lifshitz formula,
and including a rederivation of the Casimir-Polder forces. A great deal of
attention is given to the recent controversy concerning temperature corrections
to the Casimir force between real metal surfaces. A summary of new improvements
to the proximity force approximation is given, followed by a synopsis of the
current experimental situation. New results on Casimir self-stress are
reported, again based on $\delta$- function potentials. Progress in
understanding divergences in the self-stress of dielectric bodies is described,
in particular the status of a continuing calculation of the self-stress of a
dielectric cylinder. Casimir effects for solitons, and the status of the
so-called dynamical Casimir effect, are summarized. The possibilities of
understanding dark energy, strongly constrained by both cosmological and
terrestrial experiments, in terms of quantum fluctuations are discussed.
Throughout, the centrality of quantum vacuum energy in fundamental physics in
emphasized.
