Ash, tephra, and gas ejected during explosive eruptions pose a major far-reaching threat to population, health, and air traffic. Lava flows, lahars, and floods from ice-capped volcanos, as well as landslides that have a potential for tsunami generation if they reach into sea or lakes, can also have a major influence. Remote sensing contributes to the mitigation of these hazards through the use of synthetic aperture radar interferometry (InSAR) and spectroradiometry. In the case of InSAR, displacements of a volcano's surface can be interpreted in terms of magma movement beneath the ground. Thus, the technique can be used to identify precursors to eruptions and to track the evolution of eruptions. Recent advances in algorithm development enable relative displacements over many kilometers to be measured with an accuracy of only a few millimeters. Spectroradiometry on the other hand allows monitoring of a volcanic eruption through the detection of hot spots, and monitoring and quantification of the ash and SO2 emitted by volcanos into the atmosphere. The tracking of ash plumes during eruptions assists in the identification of areas that should be avoided by aircraft. Here we present a review of these two remote sensing techniques, and their application to volcanic hazards.