How effective is condom use in preventing transmission of an STD such as HIV between two people?

This is a highly politically charged subject, and you can get misinformation from all sides. I'm guessing you are talking about someone you will have sex with anyway either way, so you are absolutely crazy to ever do it without a condom. Used correctly they work very well. I think there are some a little thicker than others and I would search those out. Anal sex is the easiest way to catch AIDS, but I would also use it with oral and vaginal sex if you know or think the other person has it (get tested if you're not sure - very easy and often free!). Christian groups try to make it sound like condoms are very unsafe and break all the time, but this isn't true. Unfortunately they misuse some condom company statistics to claim this. In fact, from a legal standpoint the condom companies protect themselves legally by claiming their product is less effective than it is - that way no one can come back later and claim they were misinformed, so I think condoms work far better than even the fine print on condom boxes says.

While condoms can be effective in reducing the risk of pregnancy and STD's, they are not perfect. If everyone that used a condom didn't become pregnant, there would be a lot fewer people in the world. And STD's would be less rampant. The best prevention is abstinence. Be doubly sure if you want to take a risk -- female condom and Male condom + spermicide. But there is still a risk.

not 100% effecience againt hpv, herpes since it is too small to cover all the infected area

Condoms, when used consistently and correctly are extremely effective at preventing HIV transmission. Most people don't know how to use condoms properly. How to care for the condom before using, how to apply the condom, use lubricant !!!( which helps to prevent breakage and offers partial protection if condom breaks), and when to change condoms during sex (every 30-40 minutes). The most convincing data on the effectiveness of condoms in preventing HIV infection has been generated by prospective studies undertaken on serodiscordant couples, when one partner is infected with HIV and the other is not. These studies show that, with consistent condom use, the HIV infection rate among uninfected partners was less than 1 percent per year. Also, in situations where one partner is definitely infected, inconsistent condom use can be as risky as not using condoms at all. And I feel I must respond to the poster who suggested using a male condom, female condom, and spermicide. AHHHHH! No way should you ever "double bag" (using two condoms at once) as they can tear each other easily. (Except if there is a latex AND polyurethane allergy with one partner, than it is the better of two evils). And add spermicide to the mix??? Heres the deal on spermicide......it can increase the risk of HIV transmission and the World Health Organization and countless other bodies have recommended the removal of these products from the shelves. All lubricant manufacturers have voluntarily pulled their spermicide lube. Most condom manufacturers have stopped selling Spermicide (nonoxynol-9) lubed condoms (except two). WHO studies show that N-9 irritates the mucosal cells of the vagina and the inflammation makes it easier for HIV to gain entry to your blood supply. Spermicidally-lubricated condoms should NEVER be used for anal sex (hetero/homosexual) as it greatly irritates the lining. WHO and CONRAD studies also show that there is no statistical difference in pregnancy prevention with condoms lubricated with waterbased lube and those with spermicide as lube!!!!!! SO don't use spermicide condoms....unless you are in a monogomous relationship AND never use more than 1 condom per day (and not for anal sex, EVER). And obviously, if in the situation where you are GOING to have sex and the only condom you have is a spermicide-lubed condom.....use it before you use nothing.