This conference is the 20th of a series that starts in 1956 in Providence (USA) until the last one in Rome in 2022. It is an open window on the progress of Science in understanding the elastic, anelastic and visco-elastic behaviour of materials. Topics cover a wide domain of modern physics: crystal defect dynamics, magneto mechanical damping, dielectric relaxations, glass transition, and very low damping materials needed for gravitational wave detection and quantum opto-mechanical devices.