Three European scientists are this year's Nobel Prize winners in medicine.
They won for their discoveries of viruses that cause aids and cervical cancer.
Two French researchers helped discover the human immuno-deficiency virus, or HIV.
A German cancer researcher was honored for finding human papilloma viruses that cause cervical cancer, the second most common cancer among women.
The Nobel assembly says these discoveries helped the world understand aids, and keep the virus from spreading.
They also figured out how HPV causes cancer, leading to a vaccine.