  We sketch a particularly simple and compelling version of D-brane cosmology.
Inspired by the semi-phenomenological Randall--Sundrum models, and their
cosmological generalizations, we develop a variant that contains a single
(3+1)-dimensional D-brane which is located on the boundary of a single bulk
(4+1)-dimensional region. The D-brane boundary is itself to be interpreted as
our visible universe, with ordinary matter (planets, stars, galaxies) being
trapped on this D-brane by string theory effects. The (4+1)-dimensional bulk
is, in its simplest implementation, adS_{4+1}, anti-de Sitter space. We
demonstrate that a k=+1 closed FLRW universe is the most natural option, though
the scale factor could quite easily be so large as to make it operationally
indistinguishable from a k=0 spatially flat universe. (With minor loss of
elegance, spatially flat and hyperbolic FLRW cosmologies can also be
accommodated.) We demonstrate how this model can be made consistent with
standard cosmology, and suggest some possible observational tests.
