Optical metasurfaces are judiciously nanostructured thin films capable of manipulating the flow of light in a myriad of new ways. During the past two decades, we have witnessed a true revolution in the basic science that underlies their operation. As a result, these powerful optical elements can now deliver never-seen-before optical functions and transformed the way we think about light–matter interaction at the nanoscale. They also offer a favourable size, weight, power and cost metric compared to bulky optical elements such as lenses and prisms based on polished pieces of glass or moulded plastics. These valuable traits are especially relevant for use in many emerging applications, including wearable displays and sensors, autonomous navigation (robotics, automotive and aerospace), computational imaging, solar energy harvesting and radiative cooling. With the advent of advanced software and high-volume manufacturing processes, the promise of metasurfaces is becoming a practical reality and has already generated tremendous interest from industry. This Review discusses the rapid, recent advances towards transitioning metasurface science into real technologies, propelling the second metasurface revolution.