This work describes the application of ultrasonic air-coupled spectroscopy techniques for the characterization of materials that can not be studied by conventional water-immersion or liquid-coupling ultrasonic techniques. Specially developed air-coupled piezoelectric transducers are used. Coefficient of transmission of ultrasonic waves at normal and oblique incidence for different types of plate-shaped materials is measured and calculated in the frequency range 0.55 MHz-2.4 MHz. Resonances due to thickness mode (longitudinal and shear waves) and plate mode (Lamb waves) are observed. From these measurements and the solution of the inverse problem density, velocity, and attenuation of ultrasonic, longitudinal, shear and some Lamb waves are calculated.