At the ESRF synchrotron light source the diagnostic systems that measure and monitor the electron beam parameters cover both the Injector system (200MeV - 6 GeV, 5mA) and the 844m circumference Storage Ring (6GeV, 200mA). It is the Storage Ring diagnostics that are in constant need of the ultimate possible performances like resolution, absolute precision, speed of measurement and a wide scope of functionalities. It is for this reason that upgrades and modernizations are being conceived, planned and implemented here almost permanently on various devices and systems. These include the position monitors and their associated orbit stabilization system, the emittance monitors, the beam-loss monitors and the current and lifetime monitors. This presentation will detail their concept, their functionality and their results. This both for routine use and for special and detailed studies on the accelerator and the beam.