We discuss the radio detection technique to probe high-energy cosmic-ray or neutrino induced particle cascades. Both the direct radio emission from the particle cascade, as well as the indirect radar detection technique will be covered. We start the talk by discussing the direct Askaryan and Geomagnetic radio emission mechanisms. There will be a focus on several geometrical effects such as the Cherenkov effect, as well as Transition radiation. In the second half of this talk, the indirect radar detection technique will be discussed from both a theoretical as well as an experimental point of view.