KM3NeT is a research infrastructure, consisting of a network of deep-sea neutrino telescopes in the Mediterranean Sea. The main objective of KM3NeT is the high-energy neutrino astronomy aiming at the discovery of neutrino sources in the Universe. A cost effective technology for (very) large water Cherenkov detectors has been developed based on a new generation of low price 3-inch photo-multiplier tubes. Following the successful deployment and operation of two prototypes, the construction of the KM3NeT research infrastructure has started. A further physics perspective is the measurement of the mass hierarchy of neutrinos. A corresponding study is ongoing within KM3NeT. The prospects of the different phases of the implementation of KM3NeT are summarized.