RR Lyrae Variables in Globular Clusters and Nearby Galaxies

I point out that the Oosterhoff dichotomy for globular cluster and field RR Lyrae (RRL) stars may place the strongest constraints so far on the number of dwarf spheroidal-like protogalactic fragments that may have contributed to the formation of the Galactic halo. The first calibration of the RRL period-luminosity relation in I, J, H, K taking evolutionary effects into account is provided. Problems in the interpretation of RRL light curves and evolutionary properties are briefly reviewed.