  We present our analysis of a large sample (over 150k) of candidate Galactic
RR Lyrae (RRL) stars for which we derived high quality photometry at UV,
optical and infrared wavelengths, using data from publicly available surveys.
For a sub-sample of these stars (~2,400 fundamental mode field RRLs) we have
measured their individual metallicity using the Delta S method, resulting in
the largest and most homogeneous spectroscopic data set collected for RRLs. We
use this sample to study the metallicity distribution in the Galactic Halo,
including the long-standing problem of the Oosterhoff dichotomy among Galactic
globular clusters. We also analyze the dependence of their pulsation
properties, and in particular the shape of their infrared light curves, from
their [Fe/H] abundance.
