Islam is the world's second-largest religion, with roughly 1.6 billion Muslims in the world in 2010.
That's roughly 23 per cent of the global population.
Christianity is the largest currently, but Islam is set to overtake by 2070, according to research by the Pew Research Centre.
This is because the Muslim population is growing faster than any major religious group.
Muslims tend to have more children than members of other religious groups. Around the world, each Muslim woman has an average of 3.1 childrean, compared with 2.3 for other religions combined.
Islam also has the youngest worshippers - the median age was 23 in 2010.
This means a larger share of Muslims are ready to have children imminently and are likely to fuel Muslim population growth.
Attitudes to Islam vary across Europe, the same study found, with the UK among the most favourable to Muslims in their country.