But there currently is no cure or vaccine -- just drugs that prolong the quality and length of life -- and there is plenty of disagreement over the best way to fight the epidemic.
Current approaches stress condoms use, fidelity, or sexual abstinence.
But as many participants at this week's international AIDS conference noted, those approaches are of little use to the millions of women in the developing world at risk of infection from boyfriends or husbands.
"Married women and women who do not have control over when and even if they have sex cannot choose abstinence. And many women who have contracted HIV infections from their husbands or long-term partners were faithful. And in most cases, it's not the women's choice if male or even female condoms are used," said Zeda Rosenberg, an expert at the Bangkok AIDS conference who presented research about some new techniques that might offer hope in the fight against HIV/AIDS.
Rosenberg heads a new agency that believes vaginal gels could be such a way. Known as microbicides, these gels are designed to kill or block the HIV virus.
Early trials were a disappointment. But Rosenberg says new gels are now being developed and tested and the signs are hopeful.
"With [leadership,] sufficient financial resources, collaborative efforts and product-development expertise, we are confident that women in developing countries should have access to safe and effective microbicides within the next five to 10 years," Rosenberg said.
Another group of scientists suggested they may have already found "nature's own microbicide."
Australian researchers from Melbourne University said they found that diluted lemon juice kills the AIDS virus.
The study followed up ancient traditions in parts of Southeast Asia that lemon or lime juice can be a contraceptive.
The researchers said lemon juice may one day provide a cheap and effective form of HIV protection for poor women.
Another method up for debate was male circumcision.
South African researcher Quarraisha Abdool Karim said recent studies suggest it may have prevented HIV infection in some cases.
But Karim said other studies show no relation between circumcision and HIV rates among men.
"In other words, the current evidence is insufficient to consider male circumcision as a public health intervention," Karim said.
Not all the new research is free of controversy.
One example is tests underway by a U.S. drug company in Cambodia to see if a drug can be used as a sort of AIDS "prevention pill."
Some of the prostitutes involved will take pills with no medicinal value, to see if they contract HIV more readily than prostitutes who take the drug.
Some activists say that's putting the women at risk -- though the drug company says they are educating the women on condom use and other ways to protect themselves from infection.
Of course, a truly effective way to stop the epidemic would be through an AIDS vaccine.
But, more than two decades after the first known cases of AIDS, there is still no vaccine. And Jose Esparza, a vaccine researcher with the Bill and Melinda Gates Foundation, suggested it is still a long way off.
"During the last few years, the scientific community has come to grips with the fact that developing an HIV vaccine is probably one of the most difficult challenges that biomedical science is confronting," Esparza said.
So study on other possible ways to prevent HIV infection -- those creams, gels, pills, and circumcision -- look set to remain a priority for some time to come.