We present the state of the art on the study of surfaces and tenuous atmospheres of the icy Galilean satellites Ganymede, Europa and Callisto, from past and ongoing space exploration conducted with several spacecraft to recent telescopic observations, and we show how the ESA JUICE mission plans to explore these surfaces and atmospheres in detail with its scientific payload. The surface geology of the moons is the main evidence of their evolution and reflects the internal heating provided by tidal interactions. Surface composition is the result of endogenous and exogenous processes, with the former providing valuable information about the potential composition of shallow subsurface liquid pockets, possibly connected to deeper oceans. Finally, the icy Galilean moons have tenuous atmospheres that arise from charged particle sputtering affecting their surfaces. In the case of Europa, plumes of water vapour have also been reported, whose phenomenology at present is poorly understood and requires future close exploration. In the three main sections of the article, we discuss these topics, highlighting the key scientific objectives and investigations to be achieved by JUICE. Based on a recent predicted trajectory, we also show potential coverage maps and other examples of reference measurements. The scientific discussion and observation planning presented here are the outcome of the JUICE Working Group 2 (WG2): "<i>Surfaces and Near-surface Exospheres of the Satellites, dust and rings</i>". Non-ice Materials: Salts and Hydrates In NIMS data, non-ice materials were identified based on their spectral profiles, showing low reflectance values at wavelengths below 3 μm combined with shallow and particularly asymmetrical (distorted) water ice bands at 1.5 and 2.0 μm, as well as a relatively high reflectance in the 3–5 μm range compared to pure water ice (McCord et al. 1998a , 1998b , 1999 ). Dalton In recent years, space-based and large Earth-based telescopes such as the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) have been used to obtain spectra of Europa and Ganymede. Modern telescopic data have higher spectral resolution and lower noise than NIMS, and an intermediate spatial resolution of tens of km which is suited to highlight regional compositional trends. These data made it possible to identify irradiated sodium chloride (NaCl) on Europa (Trumbo et al. 2019a ) and to suggest that both on Europa and on Ganymede the contribution of chlorinated salts, ultimately sourced from the interior, could be larger than other endogenous chemical species such as sulphates and carbonates (Ligier et al. 2016 , 2019 ; King et al. 2022 ; King and Fletcher 2022 ). Recent laboratory experiments suggest that “hyperhydrated” sodium chloride hydrates such as 2NaCl⋅17H 2 O and NaCl⋅13H 2 O may form in the hydrosphere of Ganymede and possibly Europa and could be transferred to the surface through convective processes (Journaux et al. 2023 ). If the convective transport through the outer ice shell is efficient enough, disodium chloride decaheptahydrate (2NaCl⋅17H 2 O) is stable at ambient pressure below 235 K and may be the most abundant NaCl hydrate on the surfaces of active icy satellites (Journaux et al. 2023 ). The possible detection of 2NaCl⋅17H 2 O, for which infrared spectra still need to be acquired in the laboratory, may reveal areas where material recently upwelled from deep in the ice shell and ocean. McCord et al. ( 2001a , 2002 ) and Dalton ( 2007 ) pointed out that the Europa spectra are best matched by mixtures of hydrated mineral salts and hydrated sulfuric acid in varying proportions. McCord et al. ( 2001a , 2002 ) suggested that the mechanism could be that the Na associated with some salts could be easily swept out and that abundant H + could take its place, forming sulfuric acid. Shirley et al. ( 2010 ) and Dalton et al. ( 2012 , 2013 ) showed that on Europa the abundance of hydrated sulfuric acid on a regional scale is dominated by the energy flux of charged magnetospheric particles. Shirley et al. Data collected by the Juno/JIRAM instrument during the same flyby at an unprecedented spatial scale of <1 km/px, covering the sub-Jovian hemisphere at low northern latitudes, revealed that Ganymede exhibits local-scale variations in the composition of geological units that were formed by different mechanisms or at very different times (Tosi et al. 2024 ). Mixtures of chloride salts, bloedite and possibly carbonates may be the result of extensive aqueous alteration of silicates that occurred at some point in the history of the satellite, perhaps combined with hydrothermal activity in its depths (Tosi et al. 2024 ). 2006 ) and geysers continuously emanate smaller water ice particles and more into space (Postberg et al. 2009 , 2011a ). On Callisto, MAJIS can verify the global grain size variations indicated by NIMS (Stephan et al. 2020 ) in comparison with UVS will also perform stellar occultation measurements, during which stellar spectra are collected as the line-of-sight from UVS to the star moves through a satellite atmosphere. The presence of any UV-absorbing species such as H 2 O, O 2 , CO 2 , H 2 , CH 4 , and C 2 H 2 will modify the observed stellar signal in a predictable way, allowing the concentrations and distributions of these materials to be constrained. Similar but less frequent solar occultation measurements will facilitate searches for species absorbing at wavelengths <100 nm, where stellar flux is low due to extinction by the interstellar medium. MAJIS will also search for active plumes by observing forward scattered light from possible plume grains along the satellite limbs at high phase angle (see Sect. 4.4 ); similar observations by UVS and JANUS may also contribute to this goal. JANUS will contribute to atmospheric studies via global imaging of the sodium exosphere at Europa (EC.1d) and monitoring of optical auroral emissions at all three icy satellites.