Indoor wireless traffic is evolving at a staggering pace, and is quickly depleting radio spectrum resources. Optical wireless communication (OWC) offers powerful solutions for resolving this imminent capacity crunch of radio-based wireless networks. OWC is not intended to fully replace radio wireless techniques such as WiFi, but to complement these and offload their high traffic loads. After discussing OWC's application domains, this paper gives a tutorial overview of two major directions in OWC: wide-coverage visible light communication which builds on LED illumination techniques and shares capacity among multiple devices, and communication with narrow 2-D steered infrared beams which offers unshared high capacity to devices individually. In addition, supporting techniques for wide field-of-view receivers, device localization, bidirectional hybrid optical/radio networks, and bidirectional all-optical wireless networks are discussed.