Jupiter and Saturn's auroral emissions were first observed around 1980
using the IUE observatory and the Voyager spacecraft.  They have been
imaged at high resolution by HST, with continuing studies providing
increasing detail and information about the physical processes that drive
the outer planet magnetospheres.  The most recent observations have taken
advantage of the Cassini and New Horizons spacecraft to make comparative
measurements of the local environment close in time to HST images.  This
talk will give a brief history of the observations, summarize the
different physical conditions at Jupiter and Saturn (compared with the
Earth), and report on recent results from cross-spacecraft comparisons.