We have performed a comprehensive examination of the elliptic flow of charged hadrons produced in Cu+Cu and Au+Au collisions at √SNN = 19.6, 22.4, 64.4 and 200 GeV. We also presented the measurements of event-by-event fluctuations for Au+Au collisions at √SNN = 200 GeV. The comparison of the data from Cu+Cu and Au+Au collisions provides new information illustrating that the participant eccentricity is the relevant geometric quantity for generating the azimuthal asymmetry leading to the observed flow. The magnitude of event-by-event fluctuations agree with predictions for fluctuations of the initial shape of the collision region based on the Glauber model. These results provide qualitatively new information on the initial conditions of heavy ion collisions and the subsequent collective expansion of the system.