One of the most important tasks is to get medicine that helps Aids sufferers live longer, and is very expensive, to poorer countries where the disease is hard to stop.
In Bangladesh, thousands of people marched through Dhaka in an anti-Aids march to mark World Aids Day, which is held every year on 1 December.
Candles lit in South Africa
Other nations around the world also marked the day with events to raise awareness of the disease.
In South Africa thousands of candles will be lit and in Thailand 1,000s of people protested outside government offices.