We review recent advances in the application of dielectric whispering-gallery (WG) resonators in optics and photonics, tracing the growth of the technology from the experiments with freely flying spherical droplets of transparent liquids to integrated on-chip microresonators. Both passive (such as filters) and active (such as lasers) whispering-gallery-mode (WGM)-based devices are discussed. Problems and possible future developments in the field are outlined.