Abstract: This talk will compare and contrast results from orbiter missions to Jupiter and Saturn to study the transport and loss of mass in these giant, rotationally-influenced magnetospheres. I will focus in particular on in situ observations of magnetic reconnection and the insights that this gives us into mass circulation and mass balance. I will also show how remote observations of radio emissions and auroral displays can give a global picture of magnetospheric dynamics. My talk will finish with a summary of what we have learned from the fantastically successful Cassini mission at Saturn, and what the Juno mission may tell us about Jupiter over the next few years.