One grand challenge for materials and structures design is to satisfy multiple conflicting requirements. For example, energy infrastructure, especially those in remote and extreme environments such as offshore wind turbines and nuclear reactors, requires components to operate effectively over long time periods and avoid catastrophic failures. Structural materials in aviation must be lightweight but high in strength, stiff while dampening out harmful vibrations, survive damaging impact events, and interact with complex flows in non-detrimental ways. On smaller length scales, acoustic and ultrasonic sensors require specific frequency and dissipative responses, and need to detect wavelengths that are much smaller than their physical size. This talk focuses on a common theme to these critical engineering problems: understanding how mechanical waves interact with engineered materials across different length and time scales. In particular, the field of phononic materials studies how engineering micro- and meso-scale features in materials and structures can prescribe the frequency and spatial properties of acoustic waves. Features such as spatial periodicity of the material or geometry, resonant inclusions, and nonlinearities can lead to wave propagation and modal properties not found in natural materials. New wave propagation phenomena have been discovered in these material platforms, which has been a direct result of an interdisciplinary research approach, integrating additive manufacturing, acoustics, mechanics, materials science, and design. This presentation will discuss our group’s recent research in phononic materials, focusing on (1) effects of nonlinearity on wave propagation in phononic materials, and (2) applications of phononic materials to passive flow control, using reduced order models, finite element simulations, and experiments.