Wide Area Augmentation System or WAAS is a navigation system developed by the FAA to improve the accuracy, integrity, and availability of the Global Positioning System (GPS). The purpose of WAAS is enable aircraft to utilize on GPS navigation for all phases of flight including precision approaches.

WAAS uses a network of ground-based reference stations, located inside airports within North America and Hawaii, to measure small variations in GPS signals in the western hemisphere. The measurements are sent to master stations which send the correction messages to the WAAS satellites every 5 seconds or less. These satellites then broadcast the corrected signal back to Earth where a WAAS-enabled GPS receiver uses the corrections to compute its position with improved accuracy.

WAAS allows a precision approach to be published for any airport. Because of the improved accuracy of each GPS satellite's information, aircraft equipped with WAAS GPS are allowed to fly at lower en-route altitudes than was possible with ground-based systems.