Massive fields oscillating around their minima produce specific oscillatory patterns in the density perturbations that record the time dependence of the scale factor in the primordial Universe (hence the name 'Primordial Standard Clocks'). In this talk, I present recent developments on the model building of inflationary classical primordial standard clocks (CPSC) and emphasize their observable consequences. I then present constraints on these models from the latest Planck temperature and polarization data and show how CPSC can address anomalies at different multipoles. Finally, I discuss the prospects for detecting CPSCs with upcoming CMB missions and to distinguish them from other types of features.