During this period, the Muslim world was a collection of cultures they drew together and advanced the knowledge gained from the ancient Ancient Greece, Roman, Persian, Chinese, Indian, Egyptian, and Phoenician civilizations. The major Islamic capital cities of Baghdad, Cairo, and Córdoba became the main intellectual centers for science, philosophy, medicine, and education. The Abbasids were influenced by the Quranic injunctions and hadiths, such as 'the ink of a scholar is more holy than the blood of a martyr,' that stressed the value of knowledge. The age is traditionally understood to have begun during the reign of the Abbasid caliph Harun al-Rashid (786–809) with the inauguration of the House of Wisdom in Baghdad, where scholars from various parts of the world sought to translate and gather all the known world's knowledge into Arabic, and to have ended with the collapse of the Abbasid caliphate due to Mongol invasions and the Siege of Baghdad in 1258. The term 'Islamic Golden Age' has been attributed to a period in history wherein science, economic development and cultural works in most of the Muslim-dominated world flourished. Layla and Majnun studying together, from a Persian miniature painting. Islam is the fastest-growing major religion in the world. Sizeable Muslim communities are also found in the Americas, China, and Europe. India is the country with the largest Muslim population outside Muslim-majority countries. Muslims are the overwhelming majority in Central Asia, the majority in the Caucasus and widespread in Southeast Asia. About 13% of Muslims live in Indonesia, the largest Muslim-majority country 31% of Muslims live in South Asia, the largest population of Muslims in the world 20% in the Middle East–North Africa, where it is the dominant religion and 15% in Sub-Saharan Africa and West Africa. Most Muslims are of one of two denominations: Sunni Islam (85-90%) and Shia (10-15%), However, other denominations exist in pockets, such as Ibadi (primarily in Oman). By the percentage of the total population in a region considering themselves Muslim, 91% in the Middle East-North Africa (MENA), 89% in Central Asia, 40% in Southeast Asia, 31% in South Asia, 30% in Sub-Saharan Africa, 25% in Asia–Oceania, around 6% in Europe, and 1% in the Americas. As of 2015, 1.8 billion or about 24.1% of the world population are Muslims. (As of 2013), the combined GDP (nominal) of 49 Muslim majority countries was US$5.7 trillion, (As of 2016), they contributed 8% of the world's total. The nation states that emerged in the post-colonial era have adopted a variety of political and economic models, and they have been affected by secular and as well as religious trends. In the modern era, most of the Muslim world came under European colonial domination. All Muslims look for guidance to the Quran and believe in the prophetic mission of the Islamic prophet Muhammad, but disagreements on other matters have led to the appearance of different religious schools of thought and sects within Islam.

The history of the Muslim world spans about 1,400 years and includes a variety of socio-political developments, as well as advances in the arts, science, philosophy, and technology, particularly during the Islamic Golden Age. The term Muslim-majority countries is an alternative often used for the latter sense. In a modern geopolitical sense, these terms refer to countries where Islam is widespread, although there are no agreed criteria for inclusion. This consists of all those who adhere to the religions beliefs and laws of Islam, or to societies where Islam is practiced. The terms Muslim world and Islamic world commonly refer to the Islamic community, which is also known as the Ummah.

Most populous muslim country