This paper presents the HiFORS continuously rate shaping injector for injection pressures of 2500 bar and above developed by FEV GmbH and the Institute for Combustion Engines, RWTH Aachen University. The development process from concept definition to hydraulic and deisgn layout, material choice and manufacturing is discussed. The hydraulic operating properties are verified by injection test rig investigations. Optical investigations are conducted in an optically accessible high pressure, high temperature chamber using shadowgraphy and OH chemoluminescence detection, thereby capturing both liquid and gaseous penetration as well as combustion areas. Single cylinder investigations are carried out at a 0.4 dm3 research engine in different operating points from low part load to full load. Compared to a serial production piezo injector, base measurements using conventional square injection profiles already show reduced combustion noise at improved NOx-soot trade-off as well as lowered HC and CO emissions. Detailed investigations at part load operating points explore the potential of different continuous rate shaping patterns, while the injector’s high injection pressure capability of up to 2500 bar and its influence on engine performance is tested at full load operation points.