Sunnis are usually estimated at eighty-five to ninety per cent of the world's Muslims, and the world's Muslim population stands at roughly a quarter of humanity. That makes Sunni Islam, on any counting, the largest single religious community on earth after Christianity taken as a whole, and by some measures the fastest growing.
The demographic centre is not Arab. Indonesia, Pakistan, India and Bangladesh hold the four largest Muslim populations, and the Arabic-speaking world is a minority of Sunni Islam even though its language is the language of the Quran and its cities hold the pilgrimage. Sub-Saharan Africa is the region of fastest growth.
The internal argument that most shapes contemporary Sunni Islam runs between traditionalist currents, which insist on continuity with the classical schools and generally accommodate Sufi devotion, and reformist and revivalist currents, which appeal directly to the Quran and the practice of the earliest generations and reject a good deal of received tradition as accretion. The latter includes the Salafi movement and, in the Arabian peninsula, the tradition descending from Muhammad ibn Abd al-Wahhab in the eighteenth century, whose alliance with the house of Saud gave it the pilgrimage cities and the resources to export a particular reading. That export, funded, institutional and sustained across the later twentieth century, is one of the most consequential religious facts of the period, and it is documented rather than alleged.
A separate current, the Islamist political movements descending from the Muslim Brotherhood founded in 1928, asks a different question again: whether Islam requires a particular form of state. Sunni scholars are divided on it, and several governments in Muslim-majority countries have banned the organisations that answer yes.