Theca cells are somatic cells of the developing follicle that form an enveloping sheath around the granulosa cell layers. Activated follicles at the secondary stage of development recruit theca stem cells from the surrounding stroma cells to differentiate. Active theca cells produce androgens, which provide important hormonal communications between granulosa cells and oocytes during follicle maturation. The theca cell layer also provides structural and vascular support for the growing follicle until ovulation. Following ovulation, theca cells become a source of hormonal support for pregnancy.