  Cepheids and RR Lyrae stars are important pulsating variable stars in
distance scale work because they serve as standard candles. Cepheids follow
well-defined period-luminosity (PL) relations defined for bands extending from
optical to mid-infrared (MIR). On the other hand, RR Lyrae stars also exhibit
PL relations in the near-infrared and MIR wavelengths. In this article, we
review some of the recent developments and calibrations of PL relations for
Cepheids and RR Lyrae stars. For Cepheids, we discuss the calibration of PL
relations via the Galactic and the Large Magellanic Cloud routes. For RR Lyrae
stars, we summarize some recent work in developing the MIR PL relations.
