3D TDOA CRFS has developed an enhanced TDOA technology that can provide accurate geolocation of emitters in three dimensions using a ground-based network of nodes. This network can passively track multiple ground-based and airborne transmitters, including aircraft and UAVs, in real time to provide latitude, longitude, altitude and speed data. Our 3D TDOA solution delivers excellent accuracy; we have demonstrated passive tracking of aircraft with errors as low as a few hundred meters over a range of hundreds of kilometers and 10 km altitude. Over smaller ranges, tracking accuracy of tens of meters is feasible. Flight paths generated from 3D TDOA results can be viewed in the mapping tools of our state-of-the-art RFeye Site software, as well as being exported for overlay in Google Earth. Our 3D TDOA software is a plugin to RFeye software, which enables a network of RFeye Nodes to be used to track airborne emitters. The same Nodes can be simultaneously used for other spectrum monitoring and management missions. To provide emitter geolocation in three dimensions, a minimum of four RFeye Nodes is needed. The system can operate as a stand-alone emitter tracking system or as part of a broader UAV / airborne threat detection and defense system encompassing optical, radar, and countermeasure capabilities.