The vertical-cavity surface-emitting laser (VCSEL) is becoming a key device in high-speed optical local-area networks (LANs) and even wide-area networks (WANs). This device is also enabling ultraparallel data transfer in equipment and computer systems. In this paper, we will review its physics and the progress of technology covering the spectral band from the infrared to the ultraviolet, by featuring materials, fabrication technology, and performances such as threshold, output power, polarization, modulation and reliability. Lastly, we will touch on its future prospects.