This presentation will deal with a review of NASA's use of down-looking cloud and precipitation radars on the high-altitude ER-2 aircraft. These radars have been used for studying convection, hurricanes, clouds, and in validating satellite sensors (TRMM, CloudSat). The talk will focus on a history of the ER-2 Doppler Radar (EDOP) and Cloud Radar System (CRS) and how they have been used for various research activities. The ER-2 has been used for both precipitation and cloud process studies and the radars have been used along with other sensors such as a cloud lidar and microwave radiometers. The radars have been used for quantitative retrievals of rain rate, ice content, and other parameters. The other sensors have also been used in combination with the radars to improve or expand the dynamic range of the retrieved cloud and precipitation properties. Highlights from various field campaigns will be given from studies of hurricane hot tower, convection, and cirrus clouds. Finally, two new radars that are targeted on horizontal wind measurements in clouds and precipitation will be described.