Earth Orientation Parameters (EOPs) describe variations and irregularities in the Earth’s rotation and orientation in space. The EOPs are essential for connecting coordinates between terrestrial and celestial reference frames, ensuring consistency between Earth-fixed and space-based observations. They are fundamental to satellite-based applications, including Earth observation, communication systems, and positioning, navigation and timing (PNT) services. They are also critical for accurately pointing and operating astronomical instruments. In addition, EOPs play a central role in space mission design and operations, including launch planning, orbital insertion, rendezvous and docking manoeuvres, and the navigation and communication of spacecraft engaged in deep space exploration. Beyond operational applications, EOP time series constitute an important dataset for Earth system science. These time series capture a wide range of time-variable signals arising from the interactions between gravitational, geophysical and geodynamic processes across the Earth’s components. This provides valuable insight into the coupled dynamics of the Earth system. The following geodetic products are key to realising, monitoring and applying this Essential Geodetic Variable: