  During the past several years, experiments at RHIC have established that a
dense partonic medium is produced in Au+Au collisions at sqrt(s)=200 GeV.
Subsequently, a primary goal of analysis has been to understand and
characterize the dynamics underlying this new form of matter. Among the many
probes available, the measurements with respect to the reaction plane has
proven to be crucial to our understanding of a wide range of topics, from the
hydrodynamics of the initial expansion of the collision region to high-pt jet
quenching phenomena. Few tools have the ability to shed light on such a wide
variety of observables as the reacion plane. In this article, we discuss recent
PHENIX measurements with respect to the reaction plane, and the implications
for understanding the underlying physics of RHIC collisions.
