X-ray spectra of young supernovae (SNe) can provide information on the progenitor star and the interaction of the supernova ejecta and the circumstellar material. I will discuss some examples, with particular emphasis on SN 1998S, whose X-ray spectrum revealed for the first time in a young supernova a wealth of heavy element emission features (Ne, Al, Si, S, Ar, and Fe). By comparison with detailed calculations of supernova explosion elemental yields, these data can be used to constrain the progenitor mass. With increasingly sophisticated models and additional high quality data, application of this technique could result in many more reliable progenitor mass determinations. In addition, high resolution X-ray spectra allow us to measure the temperature evolution of a supernova and can give us a detailed picture of the progenitor’s pre-supernova evolution. As we build up additional examples from the great diversity of core collapse supernovae, we hope to come to a better understanding of the last stages of massive star evolution.