Ultrasonography is a non-invasive imaging method used for assessing pathological and physiological situations, successfully applied in the imaging of the reproductive tract of ruminants. The contribution of this diagnostic method has been essential in understanding the function of the reproductive system and especially that of the ovarian cycle. For the examination of the reproductive system of female ruminants the most frequently applied equipment is that of type B-mode real time, with linear probe and frequencies of 3.0? 5.0 and 7.5 MHz. In cattle, the examination is conducted primarily through the rectal, while in small ruminants it can also be performed transabdominal.In non-pregnant animals the ultrasound scanning aims at the examination of the cervix, the uterus and the ovaries allowing the determination of the stage of the estrus cycle, or the diagnosis of certain abnormalities of the reproductive system (ovarian cyst, anoestrus, etc). During gestation, ultrasonography finds numerous applications in ruminants, such as early pregnancy diagnosis* determination of the number and the sex of the fetuses, assessment of the stage of gestation, control of fetal vitality, etc. Ultrasonography has also been used for the selection of animals for reproduction contributing in the improvement of reproductive performance. Biotechnology is another area where ultrasound scanning is extensively used (ovum pick-up, embryo transfer, etc). Today the use of ultrasonography is widely spread in ruminants aiming at real time and dynamic assessment of the reproductive system. The cost of equipment has been reduced over the past years, enabling the veterinarians to benefit of its potentials.