We have developed a Fabry-Perot Velocity Interferometer System (F-PVIS) to measure the velocity of materials, moving with very high speeds. The F-PVIS has e.g. been applied to measure the velocity of a flyer launched by an electric gun. This gun is capable of accelerating thin plastic flyers to very high velocities (up to 8 km/s). The velocity measuring system consists of a one Watt laser, a Fabry-Perot etalon with lenses, a rotating-mirror streak camera and fiber optics to optically connect the laser and the F-P etalon to the object to be measured. The total system very efficiently handles the available light, and is able to measure velocities in the range of 100 m/s to several km/s. Currently we are able to perform two kinds of velocity measurements: (1) The evolution of the velocity of the flyer during the acceleration process. This kind of measurement is performed to calibrate the velocity of the flyer as a function of the voltage on the capacitor bank of the electric gun and as a function of the thickness, diameter and specific mass of the flyer. (2) The time resolved particle velocity at the interface of a sample, subjected to a shock wave, and a transparent material like PMMA or quartz. From the interface velocity the pressure in the sample can be determined, both for inert, solid materials and for detonating substances. With a minor modification in the above mentioned set-up we can also measure the particle velocity in a ceramic powder. Recently we also succeeded in measuring the particle velocity of the tip of a multimode quartz fiber, inserted into an explosive sample. Interpretation of this measurement is still a problem.