  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.
