This is a brief review of liquid scintillators, an important technology for detection of ionizing radiation. We will first review the basic mechanisms of light production in most organic liquid scintillators. For most practical detector applications, the scintillators need to be optimized for choices of photosensors and compatibility with optical windows. A summary of important past experimental projects with liquid scintillators is provided. We will complete the review with a list of modern practices, particularly of metal doping, and development of water based hybrid materials that allow simultaneous detection of Cherenkov and scintillation light.