Electromagnetic (EM) sounding of planetary bodies other than the Earth was first possible on the Moon, but has since been used to probe interior structure of planets and moons throughout the solar system. This emergence has been facilitated by the growing availability of mission data and associated improved understanding of planetary magnetic field environments. In this review, I outline the general principles of EM induction, with particular emphasis on planetary specific assumptions and aspects that have to be considered in non-terrestrial environments, including limited or incomplete datasets. I review magnetic field mission data from past and ongoing space missions that can support EM investigations. The availability and quality of such data determine the scope and depth of investigations, ranging from characterizing most interior layers to identifying subsurface oceans. Looking ahead, upcoming missions will facilitate a better characterization of planetary bodies, which will contribute to addressing most fundamental questions, including the possibility of oceans and potential for life within the Jovian system. In this review, I outline the general principles of EM induction, with particular emphasis on planetary specific assumptions and aspects that have to be considered in non-terrestrial environments, including limited or incomplete datasets. I review magnetic field mission data from past and ongoing space missions that can support EM investigations. The availability and quality of such data determine the scope and depth of investigations, ranging from characterizing most interior layers to identifying subsurface oceans. Unknowns range from large-scale structure and composition of planetary bodies, e.g., the presence of a core, to more specific questions such as the presence of an ocean or interior abundance of volatiles. Generally, the abundance of volatiles in our solar system is of great importance. In the case of Mars or Venus, it is unclear what happened to the water that once existed; did it escape to space or is it captured in the crust? What plays a role in the emergence of plate tectonics? Because no combined electric and magnetic field measurements have enabled MT studies so far, the focus for inner solar system bodies is on (a) understanding and approximating the inducing field, i.e., the external magnetic field environment, or (b) the use of an additional spacecraft which measures the inducing field concurrently (Grimm and Delory 2012 ). For outer solar system bodies, the sparsity of data typically limits EM studies to testing specific hypotheses, such as the existence of a highly conductive layer, as expected for a subsurface ocean. Generally, the penetration depth of electromagnetic waves depends on the period, T, and the material they propagate through. As the first mission in orbit around Jupiter, Galileo provided evidence of induction signals attributed to subsurface oceans of the Galilean moons Io, Europa, Callisto, and Ganymede (Kivelson et al. 1992 ). After its interplanetary cruise, Galileo entered three mission phases, the primary tour (1995–1998), the Galileo Europa Mission (1998–2000), and finally, the Galileo Millenium Mission (2000–2003), all focused on studying Jupiter and its moons with a focus on Europa in the second mission phase (Fig. 5 ). Fig. Compared to Apollo-era studies, the use of higher precision instruments, long-duration time series, and advanced computational techniques offers a unique opportunity to revisit outstanding questions with significantly improved accuracy and resolution. Such questions include the presence of a partially molten basal layer (Grimm and Delory 2012 ) or possible compositional heterogeneity within the lunar interior, possibly suggesting incomplete magma ocean mixing and a complex thermal evolution. 2000 ), underlining the importance of EM sounding in exploring planetary bodies. A renewed focus on those bodies is especially timely due to upcoming missions, such as JUICE and Europa Clipper, that will provide critical new datasets to further explore the presence and properties of these hypothesized oceans. Europa’s distinctly characteristic surface shows cracks across an 80–170 km thick icy surface. Multiple lines of evidence support the idea that this ice layer overlies an ocean (Pappalardo et al. 1999 ). Callisto and Ganymede might also host a subsurface ocean, although their internal structures remain more uncertain and continue to be debated (Khurana et al. 1998 ). ( 1939 ) and Srivastava ( 1966 ), then summarized in the context of planetary-scale problems (Parkinson 1983 ) was proposed by Zimmer et al. ( 2000 ); this study remains the basis for the literature in the field. Generally, a perfectly conducting ocean would induce the largest response, with an amplitude equal to the inducing field. In this case, the ocean would fully shield the interior from A self-consistent induction model including a three-layer shell, comprising a core, mantle, and subsurface ocean, surrounded by an insulating crust and plasma currents, provided better constraints on Europa’s interior (Schilling et al. 2007 , 2008 ). This model supported ocean conductivities of at least 0.25 S/m of 100 km thickness. These results are consistent with the presence of a liquid saline ocean, effectively ruling out scenarios involving either a frozen or soft ice layer. While all previous work relied on the synodic rotation period, Seufert et al. These geysers are believed to originate from a subsurface ocean beneath Enceladus’ icy crust. The ocean, likely salty and in contact with the moon’s rocky core, may contain hydrothermal vents, providing a potential habitat for life. The interaction between the ocean and the core could supply the necessary chemical ingredients and energy sources to support microbial life Ermakov et al. ( 2021 ). Titan, Saturn’s largest moon, also presents strong evidence for a subsurface ocean (e.g., Sohl et al. 2003 ).