We consider multiwavelength observations of Broad Absorption Line (BAL) QSOs which include optical spectrophotometry supplemented by HST-FOS UV spectrophotometry and/or ROSAT-PSPC x-ray observations. For moderate to high redshift objects, increasing the wavelength coverage into the UV permits observation of BALs due to different ions of the same element for several different elements for the first time. By employing appropriate assumptions, ionic column densities as a function of outflow velocity can be derived from these observations, resulting in constraints on the level of ionization and chemical composition of the BAL region (BALR) gas and the photoionization model itself.