Directed differentiation is primarily applied to pluripotent stem cells (PSCs) of mammalian origin, in particular mouse and human cells for biomedical research applications.  Since the discovery of embryonic stem (ES) cells (1981) and induced pluripotent stem (iPS) cells (2006), source material is potentially unlimited.
Historically, embryonic carcinoma (EC) cells have also been used. Fibroblasts or other differentiated cell types have been used for direct reprogramming strategies.