The ion speciation of ionic liquids dissolved in molecular liquids of low and medium polarity is studied experimentally and theoretically. The ion speciation in some representative systems is characterized by dielectric relaxation spectroscopy and electrical conductance measurements. A corresponding-states approach is used to compare the experimental results with predictions for a reference system of charged hard spheres in a dielectric continuum. Topics of special interest are the formation of ion pairs and larger ion clusters in dilute solutions and their fate at high concentrations, where they have to redissociate in the excess ionic liquid to form the charge-ordered structure of the fused salt. In solvents of low polarity this transition leads to electrical conductance minima and liquid-liquid immiscibilities.