2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/10921In this lecture I will review some recent progress in improving the accuracy of the calculation of density perturbations resulting from inflation.21-page LaTeX file for proceedings of the Erice School ``Astrofundamental Physics.'' Four postscript figures, figi.ps (i=1 to 4), included using epsfAstrophysicstext