Performant beam diagnostics are a crucial requirement for the operation of a high-current facility to achieve its design parameters. The usage of standard and advanced beam instrumentation is reviewed. In the first part of the lecture, the methods beam current, transverse profile, and emittance are presented. Invasive diagnostics, such as screens, wire scanners, and grids, may be destroyed by the high beam power; hence, the use of non-invasive types, such as Ionisation Profile Monitors and beam-induced fluorescence, is beneficial. Due to the significant non-linear contributions for high-current beams, the emittance determination is discussed with the focus on tomographic reconstruction.