  The first part of this article summarizes the evidence for Dark Energy and
Dark Matter, as well as the naturalness issues which plague current theories of
Dark Energy. The main point of this part is to argue why these naturalness
issues should provide the central theoretical guidance for the search for a
successful theory. The second part of the article describes the present status
of what I regard as being the best mechanism yet proposed for addressing this
issue: Six-dimensional Supergravity with submillimetre-sized Extra Dimensions
(Supersymmetric Large Extra Dimensions, or SLED for short). Besides summarizing
the SLED proposal itself, this section also describes the tests which this
model has passed, the main criticisms which have been raised, and the remaining
challenges which remain to be checked. The bottom line is that the proposal
survives the tests which have been completed to date, and predicts several
distinctive experimental signatures for cosmology, tests of gravity and for
accelerator-based particle physics.
