This week in Washington, the likes of Elton John and Bill Gates are mingling with AIDS activists and scientists from around the world, at the 19th International AIDS Conference.
The mood has been upbeat.
Many say there's a sense of progress in the fight against HIV.
But on the other side of the world, about a thousand sex workers are holding a parallel AIDS conference – in protest.
US law restricts sex-workers from entering the country, and those who've gathered in the Indian city of Calcutta say they want an end to that kind of discrimination.
Most AIDS experts believe including sex-workers in discussions of HIV prevention is essential if the epidemic is to be stemmed.