In recent years several reviews of 4 He nanodroplets (HNDs) have been published in this Journal. The present one focuses on the solvation of atomic, molecular or cluster ions X ± in HNDs. After briefly reviewing the properties of so-called snowballs in bulk helium we discuss experimental conditions for the efficient synthesis of charged, doped HNDs. We show that the cluster ions observed in conventional mass spectrometers originate from fission of highly charged HNDs. Mass spectra of alkali clusters recorded near the ionization threshold of HNDs reveal the size limit beyond which the neutral cluster will be fully embedded in the HND. The abundance distributions of He N X ± ions solvated in helium frequently reveal local anomalies or magic numbers. We demonstrate that the ion abundance is approximately proportional to the dissociation energy D N = E N − E N −1 . A compilation of observed magic numbers will be presented together with theoretical data, including data for ions solvated in molecular hydrogen. Alternative methods to forming He N X + that do not rely on nozzle expansions will be summarized. Electronic excitation spectra of C + 60 and polycyclic aromatic hydrocarbon ions with up to 100 adsorbed helium atoms reveal the properties of the helium adsorption layer in quantitative detail. Next we discuss theoretical efforts to describe the interaction between ions and helium. We close with summarizing the size dependence of physical quantities computed for atomic alkali and alkaline earth cations in helium, such as binding energy, superfluid fraction, structural order, radial density profiles, and the existence of first and higher solvation shells.