High-performance, optical phased arrays for electronic control of laser beams have recently been demonstrated. The optical aperture is lithographically fabricated to form a unity-fill-factor array of liquid-crystal-based optical phase shifters. The liquid-crystal phase shifters can be fabricated smaller than a wavelength of light, with spacings equally small, although this is not required in these devices for small angle steering applications. Computer control of the individual phase shifters establishes a phase profile across the optical aperture that steers or otherwise controls an incident optical beam. Prototypes of such optical phased arrays have been used to demonstrate electronically programmable optical beam steering, lensing, fanout, and conditioning. The devices offer high pointing accuracy and resolution in a small size, owing to the much shorter wavelength of light as compared to microwaves. This inertialess technology makes available to optical systems many of the performance capabilities and the functional versatility long afforded microwave systems by microwave phased array antennas. Operation of such optical phased arrays has been successfully demonstrated from the green (doubled Nd:YAG lasers) to the long-wave infrared (carbon dioxide lasers). The capability represents a major technological advance and is expected to enable numerous new optical systems. This paper focuses on a comparison of the new optical phased array technology with that of conventional microwave phased arrays. Operating principles are briefly reviewed from dual perspectives: namely, those of the microwave and optical regimes. A brief discussion of system applications is included.