In this chapter, we describe a novel understanding allowed by use of diluted magnetic semiconductor as a material in quantum wells with carrier gas. We discuss how the possibility of spin polarization of the 2D carrier gas gave new insight into both interband and intraband excitations allowing for spin resolution in the interactions. Two principal experimental tools will be used: interband spectroscopy (photoluminescence and transmission or reflectivity) and electronic resonant Raman scattering, for probing, respectively, interband and intraband excitations in systems with 2D carrier gas. Effects of carrier–carrier interactions are analyzed, e.g., charged exciton formation and many-body enhancement of Zeeman splitting.