Accurate knowledge of crack location and size around fastener sites would improve decision-making concerning maintenance actions, reduce unnecessary teardowns, minimize maintenance induced damage, and provide key information for prognostics programs.   The primary difficulty for sizing cracks around fastener sites concerns extracting reliable quantitative measures associated with crack location and size that are also insensitive to the vast array of variable conditions concerning part geometry and condition, material properties, flaw morphology, and the measurement system.  Several case studies are presented exploring quantitative NDE approaches for sizing fatigue cracks in aircraft structures using computational methods.  First, the use of feature extraction and signal classification algorithms is demonstrated for crack characterization with invariance to noise features for eddy current inspection of fastener sites.  Using simulated studies, a promising feature extraction method with broad noise invariance is presented associated with changes in the eddy current response in the circumferential direction.  Application of this approach to experimental data is also presented demonstrating the ability of this measure to potentially size cracks around fasteners.  Second, the problem of sizing cracks using ultrasonic measurements around fastener sites in multilayer structures is explored.  Of particular interest toward gaining a better understanding of this complex 3D ultrasonic scattering problem is the spiral creeping wave, which originates from the incident shear wave and propagates around the fastener hole.  Numerical models are presented to study the 3D scattering from holes with cracks to evaluate potential features for crack sizing.  Lastly, the problem of sizing cracks around fastener sites with limited accessibility relative to an ultrasonic transducer is discussed.   Models and signal processing methods are presented providing insight into the potential to size fatigue cracks around fastener holes in vertical riser structures through an angled-beam shear wave inspection.  Concepts for extension of this approach to in situ sensors will also be discussed.