There is a need for improved nondestructive evaluation (NDE) capability to characterize corrosion at faying surfaces in multi-layered aircraft structures to better support fleet management decisions and minimize cost and aircraft disassembly.  While NDI techniques are capable of detecting thickness loss at multiple interfaces, they have difficulty quantifying material loss in multiple layers for a specific lateral position, and have not readily addressed the problem of characterizing subsurface pitting corrosion and stress corrosion cracking.  The use of multiple NDE methods such as ultrasonic and eddy current have demonstrated the potential of acquiring complementary information to benefit corrosion characterization; however, manual interpretation of multiple data sets can be challenging for an inspector.  This work presents the development of data fusion methods to combine data acquired at multiple frequency (or time) scales or using multiple NDE methods for improved corrosion characterization.  The application of both empirical and model-based approaches are highlighted in this study.  Statistical data fusion methods based on Dempster-Shafer (DS) theory are shown to fuse data at the pixel level from both conventional eddy current and pulsed-eddy current techniques for either multiple frequency levels or time scales respectively.  Experimental results for the application of this approach to aircraft corrosion material loss quantification are presented.  A model-based data fusion method is also presented for incorporating ultrasonic and eddy current data and NDE models to better characterize pits in first and second layers.   Ultrasonic data is used to provide data on first layer corrosion to simplify the second layer eddy current inversion problem.  Excellent results have been achieved through validation of the methodology with simulated and real pitting corrosion samples.  Lastly, a hybrid approach incorporating both empirical and model-based data fusion methods is discussed to ideally address the corrosion characterization problem.