Atti di convegno del Nono Simposio Internazionale sulla Modellistica in scala (ISSM9) This volume contains the works presented at the ninth edition of the symposium on scale models, ISSM9. The symposium brought together 53 scientists from 8 different countries and 3 continents, from both Academia and Research Centers; they participated virtually or in person to present the latest developments and trends in scale application and progress in several engineering fields (mostly in continuum mechanics and fluid dynamics). During the symposium there were 4 keynote talks, its related abstracts are here enclosed too. The contents of the talks are about the state-of-the-art of similitude theory and scale modeling and they are useful for any researcher interested in similar topics.