Ovaries are part of the reproductive system of female organisms. In vertebrate animals, the ovaries also produce and release sex hormones which govern physical characteristics and fertility. Ovaries are extremely important because they ensure the continued survival of the species by producing ova, or eggs, which are intended for fertilization. In humans, ovaries around the size of an almond, and human females are actually born with all of the eggs they will ever have.

The specifics of ovaries vary, depending on the type of organism under discussion. In vertebrates, ovaries are attached to the fallopian tubes, which are in turn connected to the uterus. During a cycle known as ovulation, the ovaries release a single egg into the uterus. If the egg is fertilized, it will implant and develop into an embryo which will ultimately become a baby. If the egg is not fertilized, the uterine lining is shed, along with the egg, allowing the uterus to prepare anew for a fresh egg.

In addition to producing and releasing eggs which contain genetic material needed for reproduction, the ovaries also create sex hormones like estrogen and progesterone. These hormones help to regulate the ovulation process, and they also contribute to general physical characteristics associated with the female sex, such as the development of breasts. Levels of these hormones fluctuate, depending on the age of the female and where she is in her ovulation cycle.

Healthy ovaries are very important for reproductive health. Many women have annual exams to ensure that their reproductive organs, including the ovaries, are in good health; cancer is a major concern for many women, since it can impact fertility as well as overall health. Damage to the ovaries may also lead to abnormal hormone levels, which can cause mental distress and uncomfortable physical symptoms. Women who note irregularities in their menstrual cycles should contact a doctor, as these irregularities may be symptoms of more serious health problems.

Incidentally, birth control pills work by manipulating the levels of a woman's sex hormones to trick her body into thinking that an egg has already been released into the uterus. Since no egg has in fact been released, the woman cannot get pregnant. She will, however, have a period, since the dosage of hormones fluctuates to allow her uterus to shed its lining. Some birth control pills use different hormone levels, allowing women to have periods less frequently. The long term impact of these methods has not been fully explored.