The absorption line spectra of some QSOs are similar to the absorption line spectra imposed by the interstellar medium in our own galaxy on the spectra of hot stars (see Figure 1). the spectra of other QSOs show P Cygni profiles similar to those of hot stars with mass outflow (see Figure 2). the absorption lines in both of these types of spectra are due to the resonant transitions of hydrogen and of the more abundant elements.