  Variable stars have a unique part to play in Galactic astronomy. Among the
most important of these variables are the Cepheids (types I and II), the RR
Lyraes and the Miras (O- and C-rich). The current status of the basic
calibration of these stars in their roles as distance, structure and population
indicators is outlined and some examples of recent applications of these stars
to Galactic and extragalactic problems is reviewed. The expected impact of Gaia
on this type of work is discussed and the need for complementary ground based
observations, particularly large scale near-infrared photometry, is stressed.
