Several ice-rock worlds demonstrably have or are likely to possess liquid water in their interiors as well as activity on their surfaces. Europa has a liquid water ocean; Ganymede a perched liquid water ocean, Titan has stable hydrocarbon seas, and Enceladus pockets or regions of subsurface liquid water. Comparative studies of the astrobiological potentials of these worlds based on past observations provides a rich array of questions and challenges that should be addressed by the next generation of planetary missions.