The Earth's varying rotation is measured by a number of space geodetic techniques, individually or in combination. The results are reckoned as the Earth orientation parameters (EOP), which result from the intersection of the terrestrial, Earth fixed, and the celestial, space-fixed, reference frames. Conventionally, variations of the EOP are expressed by 5 parameters to describe precession/nutation, the rate of change of axial rotation, and polar motion. As the accuracy and the temporal resolution of the EOP determinations have steadily improved over recent years, we have been seeking more detailed explanations for their excitations. Besides tidal influences from outside the Earth, the principal causes for variable EOP appear to be related to the changing motions and mass distribution of the fluid portions of the planet. Observations of the geophysical fluids, such as the atmosphere, oceans, and other hydrological reservoirs, have achieved a new maturity, as they are typically combined within the context of dynamically designed fluid models, often through optimal methods of data assimilation. Independent observations of the relevant mass fields include the result of recent gravity missions like GRACE as well. Besides contemporary determination of the EOP and the related geophysical excitations, are forecasts of these quantities, important especially for the operational determination of Earth position for spacecraft navigation; the effort to improve predictions itself currently is a topic of strong interest. We seek contributions to this session that highlight new determinations of EOP series and their analyses, including combinations of different observing techniques. We also invite new discussion of the dynamical basis for links between Earth rotation, geophysical fluids, and other geodetic quantities, such as the Earth gravity field or surface deformation. Here an important example is the development of inverse methods for the determination of Earth system quantities from observations. We also welcome contributions about the relationship between EOP variability and current or potential variability in fluids due to climate variation or global change signals, including those inferred from models. In addition, we will welcome input on the characteristics and variability of the rotation parameters of other planets or planetary bodies.