The interaction between light and mechanical motion in nanostructures has become a research topic with significant impact and promise recently. This rapidly developing area at the intersection between nanophysics and quantum optics is also known as “cavity optomechanics”. Fundamental investigations in quantum physics and possible applications like ultrasensitive detection of small displacements, forces and masses drive this field. By now, the basic features have been demonstrated in various experiments worldwide during the past five years. These include displacement detection with precisions down to the standard quantum limit, nonlinear dynamics in optomechanical self-oscillations, and cavity-assisted optomechanical laser-cooling of vibrational modes. The concepts involved are general enough to be applicable to a large variety of different setups, extending to variants such as nanomechanical resonators in superconducting microwave circuits and clouds of cold atoms.It is now time to put these basic elements together and investigate the design of structures containing multiple interacting optical and mechanical modes. These could be used to form optomechanical “circuits” or “arrays”. Recently demonstrated nanofabricated photonic-phononic crystal structures provide one essential platform in which to realize these ideas. On the applied side, integrated optomechanical circuits might combine several functions, such as detection, amplification and general signal processing, or contribute to quantum information processing by converting information to and from the light field. On the fundamental side, arrays of optomechanical elements could be used to study the collective many-body dynamics (both classical and quantum) of these novel nonequilibrium systems. We propose to explore theoretically these possibilities, providing a guide-line for experiments and thereby unlocking the potential of such devices.