The main characteristics of ZnSe as material for substrates are compared with those of other classical substrates such as InP, GaAs, Si or (Cd, Zn)Te. The role of ZnSe substrates for the growth of epitaxial ZnSe layers is discussed. ZnSe bulk crystal growth is reviewed and the reasons for the poor crystalline quality of ZnSe are analysed. This has led to some suggested approaches to the growth of twin-free ZnSe crystals either by doping or by low-temperature growth. Finally the future of ZnSe as a substrate is considered.