Human immunodeficiency virus or HIV, is the virus that causes AIDS. AIDS is the final stage of HIV infection, when your body can no longer fight life-threatening infections. HIV attacks the immune system and weakens your ability to fight infections and disease. There is no cure for HIV, but there are treatments to enable most people with the virus to live a long and healthy life. The best way to prevent HIV is to use a condom for sex and never share needles or other injecting equipment.