Adherence to Islam is a global phenomenon: Muslims predominate in some 30 to 40 countries, from the Atlantic to the Pacific and along a belt that stretches across northern Africa into Central Asia and south to the northern regions of the Indian subcontinent.

Arabs account for fewer than one-fifth of all Muslims, more than half of whom live east of Karachi, Pakistan.

The most populous Islamic nation is Indonesia. 

Despite the absence of large-scale Islamic political entities, or dominant nations, the Islamic faith continues to expand, by some estimates faster than any other major religion.

A very broad perspective is required to explain the history of today's Islamic world.

Any approach to understanding Islam must go beyond the political divisions of the Islamic world in order to draw a comprehensive picture of the stages by which successive Muslim communities, throughout Islam's 14 centuries, encountered and incorporated new peoples so as to produce an international religion and civilization.

Islam is an international religion tied together by the Quran and and faith in the Prophet, Muhammad.

In spite of this seeming unity, the Muslim faith is divided along sectarian and socio-political lines.
There are approximately 1,000,000,000 Muslims:
    900,000,000 are Sunni Muslims (Saudi Arabia and Afghanistan, for example)
     40,000,000 are Shi'ite Muslims (Iraq and Iran for example)

Sufi Islam is a mystical form of Islam that is found in a variety of forms and is embraced in some cases by both Sunni and Shi'ite Muslims.

Although Christians tend to date Islam according to the Gregorian (Christian calendar using such terms as BCE and CE or AD, the Muslim calendar is dated from the Hajj or Muhammad's flight from Mecca to Medina, which corresponds to July 16, 622, in the Gregorian calendar. Muslims will date their calendar such as 100 AH (Anno Hegira or Hajj, that is, the year of the Hegira). 

The term Islamic refers to Islam as a religion.

The term Islamicate refers to the social and cultural complex that is historically associated with Islam and the Muslims, even when found among non-Muslims.