On 5 June 1981, the first case study detailing an unusual cluster of pneumonia cases among gay men alerted the world to Aids.
The red Aids ribbon, introduced in 1991, is now universally recognised
Here are some of the key dates in the history of the illness since then.
1982 - Aids, Acquired Immune Deficiency Syndrome, is first used as a term.
The condition had earlier been known as Grid - Gay Related Immune Deficiency.
The first case of Aids is reported in Africa.
1983 - The US Centers for Disease Control adds female partners to the list of groups at risk.
1984 - HIV (human immunodeficiency virus) is isolated by Luc Montagnier of the Pasteur Institute in Paris and Robert Gallo of the US National Cancer Institute.
1985 - Hollywood star Rock Hudson is revealed to have Aids.
1987 - The UK government's "Don't Die of Ignorance" campaign is launched.
Rock Hudson was revealed to have Aids in 1985
Needle exchanges are first piloted in the UK.
The first antiretroviral drug, AZT, is approved in the US.
Pictures of Princess Diana holding the hand of a patient in an Aids ward are broadcast around the world.
HIV testing is introduced across the UK.
1988 - First World Aids Day.
1989 - The first HIV awareness materials targeted at gay men are produced by the Health Education Authority.
1990 - The BBC soap opera Eastenders runs a storyline in which Mark Fowler, a major character, is found to be HIV positive, raising awareness of the condition.
Eastenders highlighted HIV in its 1990s storyline
1991 - Freddie Mercury, lead singer of Queen, dies of an Aids-related illness.
The Red Ribbon becomes the international symbol of HIV.
The US Food and Drug Administration licences the first rapid HIV test.
Ten million people around the world are HIV positive. Aids kills more men aged 25 to 44 than any other condition.
1995 - There is an outbreak of HIV among injecting drug users in Eastern Europe.
The first combination therapy - HAART, (highly active antiretroviral therapy) is approved for use in the US.
1996 - UNAIDS is established.
1998 - Trials of a vaccine against HIV begin.
2001 - Drug companies abandon their opposition to the generic production of antiretrovirals.
2002 - The Global Fund for the fight against HIV/Aids, malaria and TB is set up.
2003 - Results of the first major HIV vaccine trial - Aids VAX - show promise.
2005 - International leaders commit to universal access to treatment at the G8 Summit in Gleneagles.
About 1.3 million people in developing countries have access to treatment.
2006 - About 38.6m people are estimated to be living with Aids worldwide.