  The recent WMAP data have confirmed that exotic dark matter together with the
vacuum energy (cosmological constant) dominate in the flat Universe. Modern
particle theories naturally provide viable cold dark matter candidates with
masses in the GeV-TeV region. Supersymmetry provides the lightest
supersymmetric particle (LSP), theories in extra dimensions supply the lightest
Kaluza-Klein particle (LKP) etc. The nature of dark matter can only be
unraveled only by its direct detection in the laboratory. All such candidates
will be called WIMPs (Weakly Interacting Massive Particles). In any case the
direct dark matter search, which amounts to detecting the recoiling nucleus,
following its collision with WIMP, is central to particle physics and
cosmology. In this work we briefly review the theoretical elements relevant to
the direct dark matter detection experiments, paying particular attention to
directional experiments. i.e experiments in which, not only the energy but the
direction of the recoiling nucleus is observed. Since the direction of
observation is fixed with respect the the earth, while the Earth is rotating
around its axes, the directional experiment will sample different parts of the
sky at different times during the day. So, since the event rates are different
when looking at different parts of the sky, the observed signal in such
experiments will exhibit very interesting and characteristic periodic diurnal
variation.
