  We suggest that compactifications on Anti-de-Sitter (AdS) spaces of type IIA,
IIB, heterotic strings and eleven dimensional vacuua of M-theory are related by
a combination of $T$ and strong/weak dualities. Maldacena conjecture relates
then all these vacuua to a conformal theory on the boundaries. Furthermore
acting with discrete groups on part of the internal spaces of these theories
will lead to further dual theories with less or no supersymmetry.
