  This document describes the authors' current research project: the evaluation
of a tower of Rankin-Selberg integrals on the group E_6. We recall the notion
of a tower, and two known towers, making observations about how the integrals
within a tower may be related to one another via formal manipulations, and
offering a heuristic for how the L-functions should be related to one another
when the integrals are related in this way. A detailed description of the E_6
tower is then given.
