Icy worlds with subsurface oceans are potentially among the most common repositories of liquid water in the Universe. Moreover, the solar system is confirmed to host a number of such worlds, notably: Europa, Enceladus, and Titan. Motivated by these considerations, this chapter examines the habitability of icy worlds from a general standpoint. The oceanic properties of Europa, Enceladus, and Titan are reviewed, followed by a simple analysis of the physical conditions in which subsurface oceans may be supported. The pathways for the formation of the building blocks of life, their assembly into polymers, and subsequent delivery to the subsurface ocean are elucidated. The possible constraints on the availability of energy sources and bioessential elements are delineated, as well as the types of organisms and ecosystems that could exist. The chapter concludes by briefly speculating about the trajectories of biological evolution conceivable on icy worlds.