  Classical Cepheid and RR Lyrae variables are fundamental tracers of cosmic
distances and stellar evolution and pulsation. Light curve analysis and
pulsation properties of these radially pulsating stars provide stringent tests
for theoretical evolution and pulsation models. I discuss a detailed light
curve analysis of classical Cepheid variables in the Galaxy and the Magellanic
Clouds at multiple wavelengths. The variation of light curve parameters as a
function of period, wavelength and metallicity is quantified to constrain the
theoretical parameters, such as, the mass-luminosity relations obeyed by
Cepheids. I briefly summarize the application of multiwavelength light curve
data for Type II Cepheid and RR Lyrae variables to study the Milky Way bulge.
