  We begin by reviewing the results on the decay of unstable D-branes in type
II string theory, and the open-closed string duality proposal that arises from
these studies. We then apply this proposal to the study of tachyon driven
cosmology, namely cosmological solutions describing the decay of unstable space
filling D-branes. This naturally gives rise to a time reversal invariant bounce
solution with positive spatial curvature. In the absence of a bulk cosmological
constant the universe always begins with a big bang and ends in a big crunch.
In the presence of a bulk cosmological constant one may get non-singular
cosmological solutions for some special range of initial conditions on the
tachyon.
