A condom is a thin cover that is put on a man's penis and used during sexual intercourse. It is normally made of latex. Condoms are a form of birth control, they can prevent a pregnancy. They can also prevent the spread of certain  sexually transmitted infections, such as  gonorrhea, syphilis, or HIV.  Another name for a condom is prophylactic sheath.

In 2009, most condoms were made of latex. For people with latex allergy, plastic condoms are available.

The first condoms were made of tissue paper. Later models were made of the intestines of animals, such as sheep. Such condoms can still be found sometimes. Certain people prefer sheepskin condoms over latex ones, because sheepskin condoms can transfer body warmth better. However they do not prevent diseases as effectively as latex condoms.

Condoms are popular for several reasons. They are inexpensive and can be bought without a prescription by either a man or a woman. They can be bought at many locations, and they are easy to use (once the couple learns how.) They have no health-related side effects for either the man or the woman, and they are one of the few types of birth control that also reduce the spread of infections.  If the couple decides to have a baby, they can stop using condoms at any time and begin trying to get pregnant with no delay.

But condoms have some disadvantages. During sex, the couple must stop to put on the condom just before beginning intercourse, which interrupts and distracts them at an exciting time. Condoms reduce the physical feelings of intercourse, especially for the man, who cannot feel the heat and sensation of the woman's vagina as much. Condoms can also reduce the emotional closeness the man and woman feel during intercourse because there is something between them. Condoms are less effective than many other types of birth control, and if a couple is in a steady relationship and are having sex very often, condoms can become more expensive to use. For these reasons, once a man and woman are in a steady relationship and are sure they are free of infection, the woman often begins to use birth control pills or some other highly effective contraceptive, after which the couple stops using condoms.

Condoms are rolled up when they are packaged, and are meant to be rolled over an erect penis.  They are most commonly made of latex, but are available in other materials.  Condoms normally have an expiration date on them.  Condoms weaken after this date, and may not work properly. Condoms are also not designed to be used more than once.

It is important to know how to use a condom before using one. If a mistake is made, the condom may not work. This happens a lot. When using a condom for the first time, it could help to try using it alone to get familiar with condoms without any danger.

Nowadays women also can use condoms. Like male condoms, they increase protection for partners from pregnancy and STD's. Female condoms look like a sheath with a flexible ring on both sides of this sheath. With these rings the condom is attached to the vagina. It covers the vagina and cervix to prevent sperm from getting inside the woman's uterus. It is necessary to know that female and male condoms should not be used at the same time. In this case, both condoms may rub against each other, and this will result in failure.

The oldest condoms ever found were from the 1640s. They were made from animal and fish intestines.[1]

There are two ways to see how effective condoms are.  They are method effectiveness, where how many couples that use the condom every time they have sex properly do not get pregnant are looked at; and actual effectiveness, where the number of people that use condoms either correctly or incorrectly and do not get pregnant are looked at. Most studies show results of effectiveness over a year.

The method failure rate of condoms is 2% per year.[2]  The actual failure rate is different in different places, and the rates can be anywhere between 10 and 18% per year.[3]

According to a 2001 study by the National Institutes of Health, correct and consistent condom use:

Other sexually-transmitted infections may be affected as well, but they could not draw definite conclusions from the research they were working with.  In particular, these include STIs associated with ulcerative lesions that may be present on body surfaces where the condom does not cover, such as human papillomavirus (HPV), genital herpes simplex (HSV), chancroid, and syphilis.  If contact is made with uncovered lesions, transmission of these STIs may still occur despite appropriate condom use.  Additionally, the absence of visible lesions or symptoms cannot be used to decide whether caution is needed.

An article in The American Journal of Gynecologic Health showed that "all women who correctly and consistently used Reality® were protected from trichomonas vaginalis" (referring to a particular brand of female condom).

The most common reason for a condom failing is that the user has not put it on properly.  A condom can also fail because it has been damaged, because the latex has weakened, or because it has come off the penis during sexual intercourse.  Something else that can cause a condom to not work, as it should, is sabotage. This can be when one of the partners wants a baby, but the other one does not. Usually they pierce a condom with a sharp object, making the condom useless. Some people see it as not ethical, because one of the two sex partners does it without the other one's knowledge. There are websites that show how to do it, if the woman wants a baby, but the man does not.

One method of testing condoms for microscopic holes involves placing the condom being tested over one conducting form with another on the other side of the condom. If the condom does not prevent an electric current from flowing between the two conducting forms, it fails the test. Holes in condoms are unlikely if proper handling conditions (see below) are followed.

Several religious communities (like Catholic Christians, Muslims, and some Protestant Christians) see problems if condoms are used: