Ion range verification in particle therapy, possibly in real time, is still an open issue to improve the treatment quality by reducing safety margins. Among the various methods that are under study or already brought to the clinics, prompt gammas offer a unique opportunity of real time control. In this chapter, we present the physical background and conditions specific for the operation environment in the clinics, followed by an overview of the various techniques relying on prompt-gamma detection that have been proposed and developed for more than a decade. Different approaches, based on imaging and non-imaging techniques, providing either integrated or differential information are described, and their maturity, limitations and clinical usefulness are discussed.