  We review how tides may impact the habitability of terrestrial-like planets.
If such planets form around low-mass stars, then planets in the circumstellar
habitable zone will be close enough to their host stars to experience strong
tidal forces. We discuss 1) decay of semi-major axis, 2) circularization of
eccentric orbits, 3) evolution toward zero obliquity, 4) fixed rotation rates
(not necessarily synchronous), and 5) internal heating. We briefly describe
these effects using the example of a 0.25 solar mass star with a 10 Earth-mass
companion. We suggest that the concept of a habitable zone should be modified
to include the effects of tides.
