This EUROMECH colloquium is aimed at gathering together the experts in the field of phononic crystals and acoustic metamaterials. The objective is to discuss the current state-of-the-art and deepen the understanding of the physics and mechanics of architected materials of broad size ranges, including the nano-, micro- and macro-scales. Phononic-based materials have recently received increasing interest of researchers due to their advanced functionalities and unprecedented mechanical and acoustic abilities, which often cannot be found in conventional materials. Constantly increasing demand for real-life engineering applications of these novel materials requires the development of reliable computational techniques for estimating the material performance in real-world environments, by considering finite structural sizes and non-trivial loading conditions, as well as the development of novel phononic configurations addressing practical requirements at target frequencies. The colloquium will provide a platform for discussion and exploration of the possibilities enabled by various computational and experimental techniques for different research areas, including physics, material and mechanical engineering, aerospace, acoustics and underwater acoustics, non-destructive material evaluation, and many others.