Laser-generated relativistic plasmas are a potential source of high-energy, ultra-short particle bunches, which are envisaged to be used for a number of different applications. To gain control over the particle pulse parameters, the monitoring of the laser-generated plasma, both with sufficient spatial and temporal resolution, is crucial. For different accelerator scenarios, e.g. for the acceleration of electrons via Laser-Wakefield Acceleration (LWFA) or of ions via Target-Normal Sheath Acceleration (TNSA) or Radiation Pressure Acceleration (RPA), suitable diagnostics are required. These lectures will describe different diagnostic methods and results from other experiments, providing a deeper insight into the physics underlying the various acceleration processes.