Over the last decades, considerable effort has been devoted in characterizing 
the shape of the quasar ionizing continuum in the ultraviolet. The ionizing 
continuum from active galactic nuclei is, in fact, of fundamental importance 
for interpreting their broad emission lines and for understanding their impact 
on the surrounding gas. Furthermore, it provides hints on how the matter is 
accreted onto the super massive black hole. I will present the first 
ultraviolet composite of quasars at high redshift (~2.4) with proper 
correction for the intervening Ly_alpha forest and continuum absorption. 
I will compare this composite quasar spectrum with previous results at lower 
redshift and discuss its implication in the context of 
photoionization disk models.