  The Milky Way Cepheid RS Puppis is a particularly important calibrator for
the Leavitt law (the Period-Luminosity relation). It is a rare, long period
pulsator (P=41.5 days), and a good analog of the Cepheids observed in distant
galaxies. It is the only known Cepheid to be embedded in a large (~0.5 pc)
dusty nebula, that scatters the light from the pulsating star. Due to the light
travel time delay introduced by the scattering on the dust, the brightness and
color variations of the Cepheid imprint spectacular light echoes on the nebula.
I here present a brief overview of the studies of this phenomenon, in
particular through polarimetric imaging obtained with the HST/ACS camera. These
observations enabled us to determine the geometry of the nebula and the
distance of RS Pup. This distance determination is important in the context of
the calibration of the Baade-Wesselink technique and of the Leavitt law.
