High power ultrasound deals with the application of high energy and high frequency acoustic waves to affect the properties of materials and systems to induce physical and chemical changes. It operates at a power range from tens to thousands watts and at a frequency range of 20 kHz to 500 kHz. High power ultrasound is distinct from low power ultrasound that is used to acquire information concerning the original state of materials and systems that is generally utilized in nondestructive testing and medical imaging where operating frequency in the range of 1 MHz to 10 MHz is used. The present lecture will provide an overview of research and technology development that was carried out in our laboratory related to use of high power ultrasonic waves for intensification of extrusion processes, decrosslinking of rubbers and thermosets, copolymerization of polymer blends and compounding and manufacturing plastics and rubber nanocomposites. In addition, a brief history of the development of novel ultrasonic extrusion equipment will be provided. The effect of ultrasonic waves on the rheological properties, molecular structure, morphology and mechanical performance of materials will be discussed along with our current understanding of mechanisms of the effect and proposed models of the processes.