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Laser generated ultrasound and air-coupled ultrasonic detectors are used to develop an inspection technique for the railroad industry. The Laser Air Hybrid Ultrasonic Technique (LAHUT) has the advantage of performing inspections without establishing contact with or the need to come close to the inspected structures. This feature makes it possible to perform dynamic inspections of tracks from a moving train and stationary wayside inspection of wheels on a passing train. The study considers the most critical flaw types in railroad tracks and wheels. Some are very difficult to detect with currently available technology, others are not possible without a handheld device. The second part of the book uses a contact ultrasonic method to monitor microstructural effects during fatigue cycling of railroad steel. Two experiments configurations are presented. One is very sensitive to microcracks. Once detected, the remainder fatigue life may be predicted. The second technique is sensitive to dislocations on an atomic level. As dislocation loop length and density begins to multiple, certain changes are detected in the velocity and attenuation of the acoustic signal.