The term Muslim world, also known as Islamic world and the Ummah (Arabic: أمة‎, meaning "nation" or "community") has different meanings. In a religious sense, the Islamic Ummah refers to those who adhere to the teachings of Islam, referred to as Muslims. In a cultural sense, the Muslim Ummah refers to Islamic civilization, exclusive of non-Muslims living in that civilization. In a modern geopolitical sense, the term "Islamic Nation" usually refers collectively to Muslim-majority countries, states, districts, or towns.

Although Islamic lifestyles emphasise unity and defence of fellow Muslims, schools and branches (see Shia–Sunni relations, for example) exist. In the past both Pan-Islamism and nationalist currents have influenced the status of the Muslim world.

As of 2010, over 1.6 billion or about 23.4% of the world population are Muslims. By the percentage of the total population in a region considering themselves Muslim, 24.8% in Asia-Oceania do, 91.2% in the Middle East-North Africa, 29.6% in Sub-Saharan Africa, around 6.0% in Europe, and 0.6% in the Americas.