This chapter reviews observation at Venus, Earth, and Mars related to ionospheric ion outflow. We compareobservations made around these three planets – Venus and Mars, which are unmagnetized, and Earth, whichis magnetized – in order to assess the protective effect of planetary magnetic fields on ionospheric ion outflow. We discuss the measured flux of outflowing ionospheric ions, the energy transfer from the solar wind to the ionosphere and the fate of outflowing ionospheric ions. Our conclusion is that there is no observational evidence that,under current conditions, Earth’s magnetic field can protect its ionosphere from losing material any better thanthe induced magnetospheres of Venus and Mars. However, extrapolating this result to geological timescale or toother planets must be made with care due to the complexity of the processes associated with ionospheric ionoutflow.