The ovarian function including follicular maturation, ovulation and corpus luteum formation is regulated by a complex control system composed of hypothalamus, pituitary and the ovary itself. These organs communicate via positive and negative feedback loops and can be considered as a functional entity. Special neurons in the hypothalamus produce gonadotropin-releasing hormone (GnRH) being delivered to the anterior pituitary lobe by the pituitary portal vessels. GnRH binds to specific receptors inducing synthesis and release of the gonadotropins FSH and LH into the circulation. After binding to their specific receptors at the ovary FSH and LH induce follicular maturation, ovulation and corpus luteum formation. The ovary responds to gonadotropin stimulation in dual fashion: secretion of sexsteroids and the liberation of a fertilizable oocyte. In addition the ovary is also able to secrete peptide-hormones such as inhibin and activin. Sexsteroids and inhibin modulate the pulsatile secretion of GnRH and gonadotropins. Cooperation of theca- and granulosa cells at the ovarian level and the corpus luteum formation are described and the significance of growth factors and cytocines is emphasized. The effects of estradiol and progesterone are highlighted by the morphological response of the endometrium. The ovary is actively involved in maintaining cyclicity, as reflected by the processes of follicular growth, follicle rupture and formation of the corpus luteum with the dramatic morphological changes involved.