Mont Blanc is covered in snow and ice all year round, even in summer. The thick layer of frozen water on top is called an ice cap. Long, slow-moving rivers of ice called glaciers creep down the sides of the mountain. The most famous one, the Mer de Glace ('Sea of Ice'), is around 7 kilometres long.
The mountain was first climbed in 1786 by two men from the French town of Chamonix. Before that, most people thought no one could ever reach the top - it was full of ice cracks and freezing winds. Today, around 20,000 people try to climb it each year, though it is still a serious challenge.
The town of Chamonix at the foot of Mont Blanc is one of the world's most famous places for mountain sports: hiking, climbing, skiing, snowboarding and paragliding. In the winter, it turns into a giant ski resort with snow so deep it can bury a small car.
The mountain is slowly changing. Because the world is getting warmer, the very top has actually been getting a little shorter each year, as the ice cap melts. Scientists measure it every two years to keep track. The 'White Mountain' is still bright white - but it has a few centimetres less snow on top than it used to.