  Quasar absorption lines have long been recognized to be a sensitive probe of
the abundances, physical conditions, and kinematics of gas in a wide variety of
environments including low-density intergalactic regions that probably cannot
be studied by any other means. While some pre-Hubble Space Telescope (HST)
observations indicated that Mg II absorption lines arise in gaseous galactic
halos with a large covering factor, many early QSO absorber studies were
hampered by a lack of information about the context of the absorbers and their
connections with galaxies. By providing access to crucial ultraviolet resonance
lines at low redshifts, deployment of HST and the Far Ultraviolet Spectroscopic
Explorer enabled detailed studies of the relationships between QSO absorbers
and galaxies. The advent of large surveys such as the Sloan Digital Sky Survey
(SDSS) has also advanced the topic by greatly improving the size of absorber
and galaxy samples. This paper briefly reviews some observational results on
absorber-galaxy connections that have been obtained in the HST/SDSS era,
including Mg II absorbers, the low-z Lyman alpha forest, Lyman limit and damped
Lyman alpha absorbers, and O VI systems.

Astrophysics