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We present some recent findings concerning the use of RR Lyrae as distanceindicators and stellar tracers. We outline pros and cons of field and clusterRR Lyrae stars and discuss recent theoretical findings concerning the use ofthe Bailey (amplitude vs pulsation period) diagram to constrain the possibleoccurrence of Helium enhanced RR Lyrae stars. Nonlinear, convective RR Lyraemodels indicate that the pulsation properties of RR Lyrae stars are minimallyaffected by the helium content. The main difference between canonical and Heenhanced models is due to the increase in luminosity predicted by evolutionarymodels. Moreover, we focus our attention on the near-infrared Period-Luminosity(PL) relation of RR Lyrae and summarize observational evidence concerning theslope of the K-band PL relation in a few globulars (M92, Reticulum, M5, OmegaCen) covering a range in metallicity of ~1 dex. Current findings suggest thatthe slope has a mild dependence on the metal content when moving from themetal-poor to the metal-intermediate regime.  Finally, we also discuss the use of RR Lyrae stars either to estimate (heliumindicator: A-parameter) or to measure (absorption and emission lines) thehelium content.

RR Lyrae the Stellar Beacons of the Galactic Structure