The instruments and diagnostic systems considered for the LHC are presented and their specifications and expected performance discussed. Their task will be to measure the essential beam properties, establish diagnosis, and give information on beam behaviour. The diagnostic systems will be essential during the running-in period. Precise and reliable information from them are a prerequisite for operational optimization.During the last years, basic design and parameters of the LHC have evolved continuously. The present description of beam instrumentation and diagnostics is based on the most recent set of nominal LHC parameters
