Islam is one of the world’s largest religions. With 1.6 billion followers, Islam is second in size only to Christianity and Islam’s large base of adherents is continuing to swell. Islam has worked to convert people since its founding, and the number of Muslims in the world is still growing. Given the ever-increasing odds of having a Muslim friend, coworker or family member, here are six things to know about Islam.

Islam is an Abrahamic Religion

Islam, Christianity and Judaism are known as the three Abrahamic religions. All three faiths trace their roots back to the story of Abraham, and both Islam and Judaism see Abraham as the founder of their religions. The holy books of both Judaism and Christianity trace their spiritual lineage back through Isaac, the son of Abraham’s wife, Sarah. Islam, however, follows the story of Ishmael, Abraham’s son by Sarah’s slave, Hagar. Muslims hold that Ishmael, Abraham’s firstborn, is the true heir of Abraham. That said, they do not dismiss the importance of Isaac to the greater story.

Abraham is not the only person that all three Abrahamic religions hold in high regard. Moses is seen to be incredibly important as well. Judaism, Christianity and Islam all recognize Moses as a great prophet and teacher. In Islam, Moses is classified as rasul, a great prophet who receives a text, set of laws or distinct revelation. He is the only prophet that God, called Allah in Islam, ever speaks to directly. Every other prophet receives dreams, visions or angelic visits.

Jesus is also seen as rasul in Islam. Moses brought the Torah and Jesus brought the Gospels to their respective peoples. Both texts are honored in Islam, and the Quran, Islam’s holy book, is seen as completing them. Interestingly, much of Jesus’ story is preserved in the Quran. For example, Jesus is born of the Virgin Mary, who is in her own right believed to be a prophet, and Jesus preaches the Gospels before being sentenced to death. The main differences between the Quran and the Bible are that Jesus is not the son of God and that He was not actually crucified. Instead, God spirited Jesus away before His death.

Muhammad is the Final Prophet

Muslims believe that Muhammad was the last prophet God will send. Muhammad is rasul like Moses and Jesus before him, but Muhammad is the “Seal of the Prophets” because God will not send another prophet before Judgment Day.

Muhammad is credited with transmitting the Quran to the people who would become the first Muslims and restoring the Ka’ba. The Ka’ba is at the center of the Hajj, the sacred pilgrimage all Muslims are called on to take. Muslims believe that the Ka’ba was built by Abraham but was later polluted by idols. Muhammad tore down the idols and restored the Ka’ba to its intended, pure state. For Muslims, seeing the Ka’ba in this life is a promise that they will see God’s face in the next.

Just as non-Christian writings attest to the existence of Jesus of Nazareth, so do non-Muslim writings attest to the life of Muhammad. Muhammad was born around 570 AD to an Arab tribe in modern day Saudi Arabia. As his father was dead, Muhammad was considered to be an orphan despite the fact that his mother was still living. When he was in his twenties, Muhammad married a wealthy woman named Khadija. A number of year after their marriage, Muhammad was told by the archangel Gabriel to convey messages about God to the Arabs. Muhammad and his followers conquered the city of Mecca and purified the Ka’ba. The Muslims conquered much of the surrounding area before Muhammad’s death in 632. Muhammad is often said to have been poisoned by a captured Jewish woman.

The Holy Quran

The Quran is the holy book of Islam and is believed to be the exact words of God. Muslims hold that the words of the Quran have never been altered but are preserved exactly as God said them through Muhammad. This perfect duplication of God’s words is in contrast with the Torah and the Gospels which are believed to have been unintentionally altered or misinterpreted over time.

The Quran is written in Arabic which is considered to be the holy language of Islam, just as Sanskrit is Hinduism’s holy language. The Arabic in which the Quran is written is said to be unique and utterly absolute, leading to the name I’jaz al-qur’an or the “Immutable Quran.” Regardless of a person’s belief system, the style of the Quran is unique. No other surviving text has the same style of language, and legend has it that attempts to create a new text in the same style failed.

Information Outside the Quran

The Quran is the Muslim holy book, but it is not considered to be the only authority on Islam. The hadiths are some sayings and behaviors of Muhammad that are not included in the Quran. The hadiths were passed down by people who knew Muhammad well and used to flesh out the allusive nature of the Quran. One of the most important transmitters of hadiths was A’isha, one of Muhammad’s numerous wives.