  Recent detections of the Integrated Sachs-Wolfe effect through the
correlation of the cosmic microwave background temperature anisotropy with
traces of large scale structure provided independent evidence for the expansion
of the universe being dominated by something other than matter. Even with
perfect data, statistical errors will limit the accuracy of such measurements
to worse than 10%. On the other hand, the extraordinary sensitivity of the ISW
effect to the details of structure formation should help to make up for the
lack of precision. In these conference proceedings I discuss the extent to
which future ISW measurements can help in testing the physics responsible for
the observed cosmic acceleration.
