There is evidence that the growth of stellar populations and supermassive black holes (SMBHs) are coupled across cosmic time: the redshift evolution of star formation rate and quasar number density are similar; SMBH masses in local inactive galaxies are correlated with the velocity dispersion of their stellar bulges. Models predict that SMBHs predominantly grow in brief quasar phases accompanied by starbursts, but on-going starbursts in luminous quasars have been difficult to quantify. There have been extensive photometric studies of quasar host galaxies. However, spectroscopic studies that provide crucial information on stellar populations such as age and velocity dispersion are scarce, especially at the highest luminosities, where the stars are vastly outshone by the quasar.