Abstract
Classical pulsating stars such as Cepheid and RR Lyrae variables are the most sensitive probes for the precision stellar astrophysics and the extragalactic distance measurements. These stellar standard candles obey well-defined period-luminosity relations which provide an absolute calibration of the first rung of the cosmic distance ladder leading to an increasingly accurate and precise local determination of the Hubble constant. Given the ongoing Hubble tension, Cepheid-independent primary calibrations are being used to not only measure the Hubble constant independently but also to better understand possible systematic uncertainties in the local measurements. I will present the recent progress in the absolute calibration of period-luminosity relations of Cepheid, RR Lyrae, and Mira variables in the Gaia era. I will also discuss our ongoing theoretical and observational efforts to quantify metallicity effects and other residual systematics in the use of classical pulsators as primary standard candles in the upcoming era of extremely large telescopes.