With an instrumented volume of one gigaton, the IceCube neutrino observatory at the South Pole is the largest neutrino detector in the world. While initially deemed impossible to observe due to IceCube's high energy threshold, the low-energy infill array DeepCore has opened up the full breadth of neutrino oscillation physics. Exploiting the ubiquitous flux of atmospheric neutrinos, IceCube now not only provides important contributions to the measurement of the atmospheric mixing parameters. The very high rate of neutrino observations also allows for worlds most precise measurement of tau neutrino appearance, stringent limits on non-standard interactions of the neutrinos as well as on the existence of sterile neutrinos. The IceCube Upgrade scheduled for the austral season 2022/2023 will further boost the sensitivity in all oscillation analyses, and — in combination with the reactor neutrino experiment JUNO — will allow to resolve the question of neutrino mass ordering at 5σ confidence level.