Abstract: The force exerted by photons is of fundamental importance in light- matter interactions. For example, in free space, optical tweezers have been widely used to manipulate atoms and microscale dielectric particles. This optical force is expected to be greatly enhanced in a nanophotonic waveguides in which light is highly concentrated with orders of magnitude larger intensity. Recently, we reported the direct detection and exploitation of transverse optical forces in an integrated silicon photonic circuit through an embedded nanomechanical resonator. We further experimentally demonstrated that this optical force is bipolar – its direction can either attractive or repulsive depending on the relative optical phase. We have subsequently exploited the optical force is a variety of photonic structures, including photonic crystal and micro-disk optical resonators. Harnessing the optical force on a semiconductor chip will allow solid state devices, such as nanoelectromechanical systems (NEMS), to operate with substantial bandwidth and design flexibility compared to conventional electrical-based schemes. In addition, examples of NEMS devices as ultrafast chemical sensors will also be described.