Classical Cepheid and RR Lyrae variables are radially pulsating stars that trace young and old-age stellar populations, respectively. These classical pulsating stars are the most sensitive probes for the precision stellar astrophysics and the extragalactic distance measurements. Despite their extensive use as standard candles thanks to their well-defined Period-Luminosity relations, distance measurements based on these objects suffer from their absolute primary calibrations, metallicity effects, and other systematic uncertainties. Here, I present a review of classical Cepheid, RR Lyrae, and Type II Cepheid variables starting with a historical introduction and describing their basic evolutionary and pulsational properties. I will focus on recent theoretical and observational efforts to establish absolute scale for these standard candles at multiple wavelengths. The application of these classical pulsating stars to high-precision cosmic distance scale will be discussed along with observational systematics. I will summarize with an outlook for further improvements in our understanding of these classical pulsators in the upcoming era of extremely large telescopes.
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