The ice giants in our solar system, Uranus and Neptune, are great analogues to a vast number of exoplanets present in the Universe. Given their relative proximity to the Earth,  we can perform detailed observations of their atmospheres, yet these planets remain some of the most poorly understood. The upper atmosphere of a giant planet plays an important role as the interface layer between the lower atmosphere below and the magnetosphere beyond. It has two basic components: the neutral thermosphere and the charged particle ionosphere. The ionosphere senses the magnetic field whilst the thermosphere is affected by dynamical processes in the lower atmosphere. Understanding momentum transfer between these systems becomes critical in understanding the energy balance of the atmosphere and magnetosphere as a coupled system. The most striking manifestation of these interactions is the aurora, observed about the magnetic poles, capable of injecting large amounts of energy into the upper atmosphere. The ionosphere can be sensed remotely via spectral observations of the molecular ion H3+ which reveal the temperature of the upper atmosphere and ion density of this region. H3+ was discovered at Uranus in 1992 and we have a 29 year baseline of observations that reveal that the upper atmosphere is subject to long-term cooling that may be related to the extreme seasons of Uranus. However, the 2007 equinox did not offer a reversal in this trend, and as of 2020 continued cooling has been observed. Surprisingly, H3+ remains undetected at Neptune, with the upper limit of the ionospheric density being much lower than predicted by models. Finally, we will discuss how future facilities, including dedicated spacecraft missions and the James Webb Space Telescope, can enhance our understanding of the ionosphere of Uranus and Neptune.