This paper describes the validation and properties of the median radial velocities published in Gaia Data Release 2 (Gaia DR2). The Radial Velocity Spectrometer (RVS) instrument on Gaia collected 280 million spectra, from which median radial velocities were derived for 9.8 million sources brighter than \( G_{\text{RVS}} = 12 \) mag. The selected sample is assessed for accuracy and precision using ground-based catalogues. The published median radial velocities cover the full sky and have a completeness of 77.2% for stars brighter than \( G \leq 12.5 \) mag. The residuals of the median radial velocities with respect to ground-based surveys vary but do not exceed a few 100 ms s\(^{-1}\). The radial velocities show a positive trend with magnitude, starting around \( G_{\text{RVS}} \sim 9 \) mag and reaching about +500 ms s\(^{-1}\) at \( G_{\text{RVS}} = 11.75 \) mag. The overall precision, estimated from the median of the Gaia radial velocity uncertainties, is 1.03 km s\(^{-1}\). The precision is influenced by parameters such as magnitude and effective temperature, with bright stars ( \( G_{\text{RVS}} \in [4, 8] \) mag) showing a precision of 200-350 ms s\(^{-1}\), which is about 3 to 5 times better than the pre-launch specification. For faint stars ( \( G_{\text{RVS}} = 11.75 \) mag), the precisions for \( T_{\text{eff}} = 5000 \) K and 6500 K are 1.4 km s\(^{-1}\) and 3.7 km s\(^{-1}\), respectively. The paper also discusses the selection criteria for publishing radial velocities, including filters for large coordinate uncertainties, faint stars, ambiguous transits, large radial velocity uncertainties, suspected double-line spectroscopic binaries, suspected emission-line stars, cool stars, and hot stars. The final catalog contains 2.6 million median radial velocities, with a distribution of radial velocity uncertainties and a median of 1.05 km s\(^{-1}\). The accuracy of the median radial velocities is assessed using five ground-based catalogues, showing a small offset and positive trend with magnitude, effective temperature, surface gravity, and metallicity. The paper also presents maps of the median radial velocities and their residuals, providing insights into the differential rotation of the Galaxy and the impact of systematic effects.This paper describes the validation and properties of the median radial velocities published in Gaia Data Release 2 (Gaia DR2). The Radial Velocity Spectrometer (RVS) instrument on Gaia collected 280 million spectra, from which median radial velocities were derived for 9.8 million sources brighter than \( G_{\text{RVS}} = 12 \) mag. The selected sample is assessed for accuracy and precision using ground-based catalogues. The published median radial velocities cover the full sky and have a completeness of 77.2% for stars brighter than \( G \leq 12.5 \) mag. The residuals of the median radial velocities with respect to ground-based surveys vary but do not exceed a few 100 ms s\(^{-1}\). The radial velocities show a positive trend with magnitude, starting around \( G_{\text{RVS}} \sim 9 \) mag and reaching about +500 ms s\(^{-1}\) at \( G_{\text{RVS}} = 11.75 \) mag. The overall precision, estimated from the median of the Gaia radial velocity uncertainties, is 1.03 km s\(^{-1}\). The precision is influenced by parameters such as magnitude and effective temperature, with bright stars ( \( G_{\text{RVS}} \in [4, 8] \) mag) showing a precision of 200-350 ms s\(^{-1}\), which is about 3 to 5 times better than the pre-launch specification. For faint stars ( \( G_{\text{RVS}} = 11.75 \) mag), the precisions for \( T_{\text{eff}} = 5000 \) K and 6500 K are 1.4 km s\(^{-1}\) and 3.7 km s\(^{-1}\), respectively. The paper also discusses the selection criteria for publishing radial velocities, including filters for large coordinate uncertainties, faint stars, ambiguous transits, large radial velocity uncertainties, suspected double-line spectroscopic binaries, suspected emission-line stars, cool stars, and hot stars. The final catalog contains 2.6 million median radial velocities, with a distribution of radial velocity uncertainties and a median of 1.05 km s\(^{-1}\). The accuracy of the median radial velocities is assessed using five ground-based catalogues, showing a small offset and positive trend with magnitude, effective temperature, surface gravity, and metallicity. The paper also presents maps of the median radial velocities and their residuals, providing insights into the differential rotation of the Galaxy and the impact of systematic effects.