The NASA Cloud Physics Lidar (CPL) has been used for validation and simulation of satellite lidar instruments. The CPL operates on the high-altitude ER-2 aircraft, thereby providing an excellent validation and simulation tool for spaceborne lidar instruments. In early 2003 CPL provided validation measurements for the GLAS instrument. Because CPL provides a unique high-altitude downward-looking lidar perspective, data from CPL has been used extensively to simulate CALIPSO lidar measurements. In this presentation we will show examples of CPL validation of GLAS measurements. We will also show examples of CPL data used to simulate various aspects of the upcoming CALIPSO mission, which will eventually lead to validation of the CALIPSO lidar. Finally, we will provide a brief introduction to CPL and other airborne data used as proxies for future A-Train measurements for the purpose of developing synergistic algorithms.