This chapter discusses the properties (band-gap energy, exciton binding energy, and lattice constant) of CdSe quantum wells. It reviews only the properties of quantum wells including strong disorder due to compositional fluctuations. Interdiffusion can lead to significant broadening of the quantum wells (QW) when CdSe is grown on ZnSe as is shown by analysis of high resolution electron microscopy. The heteropair CdSe/ZnSe has a large lattice mismatch of 6.7% leading to a critical thickness of CdSe on ZnSe of below 3 monolayers. The PL emission wavelength can be largely tuned in this strained system with maximum blue shifts of about 1eV with respect to the bulk CdSe. Island formation is studied in three regimes: (a) in the Stranski-Krastanov growth mode, (b) using deposition of fractional monolayers of CdSe, or (c) employing a thermally activated reorganization process in a narrow CdSe layer during growth interruption. The heteropair CdSe/MgS has a similar lattice mismatch as CdSe/ZnSe but a much stronger confinement. A large enhancement of the photoluminescence efficiency and a reduction of the threshold for stimulated emission is reported for laser structures incorporating a CdSe fractional monolayer QW embedded in ZnSe with respect to a (Cd,Zn)Se alloy QW. The luminescence transients observed in ultrathin CdSe/ZnSe SQWs show a fast nonexponential decay on the high-energy side and an increasingly longer, nearly exponential decay on the low-energy side of the PL spectrum. This behaviour is discussed in terms of excitons relaxing in a random potential.