In recent years, as first established in some 6 papers in Science and Nature from the PI s group, a new paradigm has emerged. This reveals the remarkable and unsuspected - role of hydration layers in modulating frictional forces between sliding surfaces or molecular layers in aqueous media, termed hydration lubrication, in which the lubricating mode is completely different from the classic one of oils or surfactants. In this project we address the substantial challenges that have now arisen: what are the underlying mechanisms controlling this effect? what are the potential breakthroughs that it may lead to? We will answer these questions through several interrelated objectives designed to address both fundamental aspects, as well as limits of applicability. We will use surface force balance (SFB) experiments, for which we will develop new methodologies, to characterize normal and frictional forces between atomically smooth surfaces where the nature of the surfaces (hydrophilic, hydrophobic, metallic, polymeric), as well as their electric potential, may be independently varied. We will examine mono- and multivalent ions to establish the role of relaxation rates and hydration energies in controlling the hydration lubrication, will probe hydration interactions at both hydrophobic/hydrophilic surfaces and will monitor slip of hydrated ions past surfaces. We will also characterize the hydration lubrication properties of a wide range of novel surface systems, including surfactants, liposomes, polymer brushes and, importantly, liposomes, using also synchrotron X-ray reflectometry for structural information. Attainment of these objectives should lead to conceptual breakthroughs both in our understanding of this new paradigm, and for its practical implications.