[en] The design of the first ITER Neutral Beam Injector (NBI) and the ITER Neutral Beam Test Facility (NBTF) is presently in progress in the framework of EFDA contracts with several European Associations. This paper deals with the design study of the diagnostics of the ITER Neutral Beam Injector and the Neutral Beam Test Facility. Starting from the list of foreseen measurements and their preferred locations, available in the existing ITER documentation, the diagnostics specifications for measurement, interlock and protection purposes were identified, in terms of measurement range, accuracy, resolution, bandwidth, operating temperature. Different diagnostics sets for the ITER NBI and the NBTF are proposed, emphasizing operational flexibility and completeness of information for the NBTF, and reliability and system protection for the NBI. All the requirements of ITER environment are considered and feasible technical solutions are identified for the majority of sensors. For both the NBI and NBTF specific environments, materials choice and sensor design are proposed, compatible with the need of obtaining the required neutron and radiation hardness, remote handling compatibility, high vacuum and tritium compatibility, and high voltage electrical insulation. This last aspect is very critical in several injector components. The feasibility study is extended from sensors to wiring, connectors and vacuum feedthroughs, identifying technical solutions with equivalent levels of compatibility and with mechanical characteristics suitable for a reliable and effective integration in injector components. This aspect of the design is very challenging due to the mechanical complexity of the components with severe geometrical, thermal and electrical constraints. For the calorimetric diagnostics of the Beam Line Components, which represent the majority of the NBI and NBTF diagnostics, a detailed design and full integration of the whole system is presented, showing the effectiveness of the technical solutions proposed. The open issues still existing for some diagnostics, to be addressed with future R(and)D activities, are also discussed in the paper. (author)