  This article gives a brief qualitative description of the possible evolution
of the early Universe between the end of an inflationary epoch and the end of
Big Bang nucleosynthesis. After a general introduction, establishing the
minimum requirements cosmologists impose on this cosmic evolutionary phase,
namely, successful baryogenesis, the production of cosmic dark matter, and
successful light-element nucleosynthesis, a more detailed discussion on some
recent developments follows. This latter includes the physics of preheating,
the putative production of (alternative) dark matter, and the current status of
Big Bang nucleosynthesis.
