Planetary interiors directly influence the habitability of their surfaces. The composition, dynamics, and stability of the atmosphere and surface environment are influenced by the tectonic mode, the thermal state, and magnetic field generation in the interior. Using Earth as a prototype, this chapter discusses the mechanisms with which the interior is thought to influence the surface, the constraints and difficulties with thermal evolution models, the potential for strong tidal effects, the importance of planetary magnetic fields, and possible surface-interior feedback. The Earth-Venus dichotomy is used to illustrate how planets with similar size and bulk composition can diverge over time and to emphasize the importance of considering the evolution of the planet as a whole (mantle plus core) where divergence may be triggered by small differences. The plausible range of rocky exoplanet magnetic field evolutions is described qualitatively in terms of the core cooling rate to illustrate how the thermal evolution is intertwined with the magnetic field. Finally, the next-generation observations and theory that are needed to progress an understanding of the role of planetary interiors on habitability and the search for life are discussed.