  During the course of stellar evolution, the location and width of the
habitable zone changes as the luminosity and radius of the star evolves. The
duration of habitability for a planet located at a given distance from a star
is greatly affected by the characteristics of the host star. A quantification
of these effects can be used observationally in the search for life around
nearby stars. The longer the duration of habitability, the more likely it is
that life has evolved. The preparation of observational techniques aimed at
detecting life would benefit from the scientific requirements deduced from the
evolution of the habitable zone. We present a study of the evolution of the
habitable zone around stars of 1.0, 1.5, and 2.0 M$_{\odot}$ for metallicities
ranging from Z=0.0001 to Z=0.070. We also consider the evolution of the
habitable zone from the pre-main sequence until the asymptotic giant branch is
reached. We find that metallicity strongly affects the duration of the
habitable zone for a planet as well as the distance from the host star where
the duration is maximized. For a 1.0 M$_{\odot}$ star with near Solar
metallicity, Z=0.017, the duration of the habitable zone is $>$10 Gyr at
distances 1.2 to 2.0 AU from the star, whereas the duration is $>$20 Gyr for
high metallicity stars (Z=0.070) at distances of 0.7 to 1.8 AU, and $\sim$4 Gyr
at distances of 1.8 to 3.3 AU for low metallicity stars (Z=0.0001).
Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.
