Cavity optomechanics(1) is a new research field that has seen spectacular advances in recent years. Optomechanics combines advances in nano-and electromechanical systems with radiation pressure enabled control. The radiation pressure backaction enables to readout mechanical motion of micro-and nanoscale mechanical oscillators with an imprecision at the standard quantum limit, enables to amplify(2) mechanical motion - enabling coherent mechanical oscillators. Likewise the cooling(3,4) of mechanical oscillators has enabled to access the quantum regime of optomechanical systems. Likewise mechanical degrees of freedom provide new ways to control the propagation of light via the phenomenon of optomechanically induced transparency(5), which can e. g. enable switching, slowing or advancing of electromagnetic pulses(6). Cavity optomechanical systems also have reached the quantum regime of mechanical oscillators, which has been long anticipated. As one example of the possible range of optomechanical phenomena, we review an optomechanical microresonator in which optical and mechanical degrees of freedom exchange energy at a rate exceeding the relevant decoherence rates in the system, enabling quantum control of a mechanical oscillator with light. Such quantum coherent coupling provided a quantum coherent link(7) between engineered microscale oscillators and the light field.