  Casimir effect is the attractive force which acts between two plane parallel,
closely spaced, uncharged, metallic plates in vacuum. This phenomenon was
predicted theoretically in 1948 and reliably investigated experimentally only
in recent years. In fact, the Casimir force is similar to the familiar van der
Waals force in the case of relatively large separations when the relativistic
effects come into play. We review the most important experiments on measuring
the Casimir force by means of torsion pendulum, atomic force microscope and
micromechanical torsional oscillator. Special attention is paid to the puzzle
of the thermal Casimir force, i.e., to the apparent violation of the third law
of thermodynamics when the Lifshitz theory of dispersion forces is applied to
real metals. Thereafter we discuss the role of the Casimir force in nanosystems
including the stiction phenomenon, actuators, and interaction of hydrogen atoms
with carbon nanotubes. The applications of the Casimir effect for constraining
predictions of extra-dimensional unification schemes and other physics beyond
the standard model are also considered.
