This paper presents new concepts in the study of folliculogenesis and describes some of the current applications to reproductive biotechnology. The importance of better understanding this issue is addressed both for basic and applied research. After a brief review of the basic conceptions of the origin, formation, and growth of follicles according to established concepts, some controversial points, as the postnatal production of the follicles and the role of multioocyte follicles, are discussed. The importance of the ovarian follicular reserve is considered for fertility and reproductive parameters, as well as some questions about the presence of multioocyte follicles in adult ovaries. Finally, some future prospects are proposed