The science of the interaction of sound and light, including acousto-optics and opto-acoustics, has recently witnessed the emergence of new topics and directions that lead to a renewed understanding of fundamental effects and to novel applications. Optomechanical structures, including phoxonic crystals, also known as simultaneous photonic and phononic crystals, are presently being investigated in order to obtain very efficient interactions in tiny volumes. Optical forces, for instance the optical pressure exerted by light on a dielectric micro- or nano-structure, can set a mechanical resonator into motion. They thus allow for the control of phonons with photons, but also for ultimate sensing applications. Concurrently, opto-acoustical interactions in micro- and nano-scale optical fibers and waveguides are being seen in a new light thanks to new materials and structures, leading to a renewed view of Brillouin light scattering.