  We compare theoretical expectations for the observation of spin correlations
in top quark pair production and decay at the Fermilab Tevatron and the CERN
Large Hadron Collider (LHC). In particular, we note that the differing top
quark pair production mechanisms in the two environments test different aspects
of the Standard Model and require different strategies to observe the
correlations. At the Tevatron, production is dominated by q qbar --> t tbar and
the strategy is to construct a double-decay angle distribution where one decay
angle is measured in the t rest frame and the other in the tbar rest frame. The
dominant process at the LHC is gg --> t tbar, with a rich spin structure that
allows for a second option in observing spin correlations. Here the strategy is
to select events where the t tbar pair is produced at relatively low velocity
in the zero momentum frame (ZMF). For these events, there are strong azimuthal
correlations between t and tbar decay products present. This measurement enjoys
the advantage that it can be carried out in the laboratory frame.
