  We briefly review the concept of a parallel `mirror' world which has the same
particle physics as the observable world and couples to the latter by gravity
and perhaps other very weak forces. The nucleosynthesis bounds demand that the
mirror world should have a smaller temperature than the ordinary one. By this
reason its evolution should substantially deviate from the standard cosmology
as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are
concerned. In particular, we show that in the context of certain baryogenesis
scenarios, the baryon asymmetry in the mirror world should be larger than in
the observable one. Moreover, we show that mirror baryons could naturally
constitute the dominant dark matter component of the Universe, and discuss its
cosmological implications.
