The scope of this SAE Information Report is to provide basic information on ultrasonics, as applied in the field of nondestructive inspection. References to detailed information are listed in Section 2. Ultrasonic testing is a versatile nondestructive inspection method which is applicable to most solid materials, metallic or nonmetallic. Materials inspected include steel, aluminum, cast iron, concrete, rubber, glass, and plastics. Through these tests, surface and internal discontinuities such as laps, seams, voids, cracks, blow holes, inclusions, lack of bond, and porosity can be detected. Material thickness can be accurately measured from one side. Under certain conditions, materials at elevated temperatures can be inspected.