  There has recently been a revival of interest in anti de-Sitter space (AdS)
brought about by the conjectured duality beteeen physics in the bulk of AdS and
a conformal field theory on the boundary. Since the whole subject of branes,
singletons and superconformal field theories on the AdS boundary was an active
area of research about ten years ago, I begin with a historical review,
including the ``Membrane at the end of the universe'' idea. Next I discuss two
recent papers with Lu and Pope on on $AdS_{5} \times S^{5}$ and on $AdS_{3}
\times S^{3}$, respectively. In each case we note that odd-dimensional spheres
$S^{{2n+1}}$ may be regarded as U(1) bundles over $CP^{n}$ and that this
permits an unconventional ``Hopf''duality along the U(1) fibre. This leads in
particular to the phenomenon of BPS without BPS whereby states which appear to
be non-BPS in one picture are seen to be BPS in the dual picture.
