The prophet Muhammad, sometimes spelled Mohammed or Mohammad, was born in Mecca, Saudi Arabia, in A.D. 570. Muslims believe he was the final prophet sent by God to reveal their faith to mankind.

According to Islamic texts and tradition, an angel named Gabriel visited Muhammad in 610 while he was meditating in a cave. The angel ordered Muhammad to recite the words of Allah.

Muslims believe that Muhammad continued to receive revelations from Allah throughout the rest of his life.

Starting in about 613, Muhammad began preaching throughout Mecca the messages he received. He taught that there was no other God but Allah and that Muslims should devote their lives to this God.

In 622, Muhammad traveled from Mecca to Medina with his supporters. This journey became known as the Hijra (also spelled Hegira or Hijrah), and marks the beginning of the Islamic calendar.

Some seven years later, Muhammad and his many followers returned to Mecca and conquered the region. He continued to preach until his death in 632.

After Muhammad’s passing, Islam began to spread rapidly.  A series of leaders, known as caliphs, became successors to Muhammad. This system of leadership, which was run by a Muslim ruler, became known as a caliphate.

The first caliph was Abu Bakr, Muhammad’s father-in-law and close friend.

Abu Bakr died about two years after he was elected and was succeeded in 634 by Caliph Umar, another father-in-law of Muhammad.

When Umar was assassinated six years after being named caliph, Uthman, Muhammad’s son-in-law, took the role.

Uthman was also killed, and Ali, Muhammad’s cousin and son-in-law, was selected as the next caliph.

During the reign of the first four caliphs, Arab Muslims conquered large regions in the Middle East, including Syria, Palestine, Iran and Iraq. Islam also spread throughout areas in Europe, Africa, and Asia.

The caliphate system lasted for centuries and eventually evolved into the Ottoman Empire, which controlled large regions in the Middle East from about 1517 until 1917, when World War I ended the Ottoman reign.

When Muhammad died, there was debate over who should replace him as leader. This led to a schism in Islam, and two major sects emerged: the Sunnis and the Shiites.

Sunnis make up nearly 90 percent of Muslims worldwide. They accept that the first four caliphs were the true successors to Muhammad.

Shiite Muslims believe that only the caliph Ali and his descendants are the real successors to Muhammad. They deny the legitimacy of the first three caliphs. Today, Shiite Muslims have a considerable presence in Iran, Iraq and Syria.

Other, smaller Muslim denominations within the Sunni and Shiite groups exist. Some of these include:

The Quran (sometimes spelled Qur’an or Koran) is considered the most important holy book among Muslims.

It contains some basic information that is found in the Hebrew Bible as well as revelations that were given to Muhammad. The text is considered the sacred word of God and supercedes any previous writings.

Most Muslims believe that Muhammad’s scribes wrote down his words, which became the Quran. (Muhammad himself was never taught to read or write.)

The book is written with Allah as the first person, speaking through Gabriel to Muhammad. It contains 114 chapters, which are called surahs.

Scholars believe the Quran was compiled shortly after Muhammad’s death, under the guidance of Caliph Abu Bakr.

The Islamic calendar, also called the Hijra calendar, is a lunar calendar used in Islamic religious worship. The calendar began in the year A.D. 622, celebrating the journey of Muhammad from Mecca to Medina.

The Islamic calendar indicates the proper days of Islamic holidays and celebrations, including the period of fasting and prayer known as Ramadan, which occurs during the ninth month of the calendar.

As in many religions, there is no single image or symbol of Islam that is universally accepted by all Muslims worldwide.

The crescent moon and star has been adopted in some predominantly Muslim countries as a symbol of Islam, though the crescent moon and star image is believed to pre-date Islam and was originally a symbol of the Ottoman Empire.

In some other applications, such as the International Red Cross and Red Crescent humanitarian aid movement, a red crescent indicates that followers of Islam are respected and treated accordingly.

The color green is also sometimes associated with Islam, as it was reportedly a favorite color of Muhammad's and is often featured prominently in the flags of predominantly Muslim countries.

Muslims follow five basic pillars that are essential to their faith. These include:

Islam’s legal system is known as Sharia Law. This faith-based code of conduct directs Muslims on how they should live in nearly every aspect of their lives.

Sharia law requires men and women to dress modestly. It also outlines marriage guidelines and other moral principles for Muslims.

If crimes are committed, Sharia law is known for its harsh punishments. For example, the punishment for theft is amputating a person’s hand. Adultery can carry the penalty of death by stoning. However, many Muslims do not support such extreme measures.

The prophet Muhammad is credited with building the first mosque in the courtyard of his house in Medina. Mosques today follow some of the same principles he established in A.D 622.

Muslim prayer is often conducted in a mosque's large open space or outdoor courtyard. A mihrab is a decorative feature or niche in the mosque that indicates the direction to Mecca, and therefore the direction to face during prayer.

Men and women pray separately, and Muslims may visit a mosque five times a day for each of the prayer sessions. In addition to hosting prayers, mosques often function as public gathering places and social centers.

The two major Muslim holidays are:

Eid al-Adha: celebrates the Prophet Abraham’s willingness to sacrifice his son for Allah.

Eid al-Fitr: marks the end of Ramadan—the Islamic holy month of fasting.

Muslims also celebrate other holidays, such as the Islamic New Year and the birth of Muhammad.

In recent years, Islam’s supposed association with terrorism and mass murder has sparked a political debate in many countries. The controversial term “radical Islam” has become a well-known label to describe the religion’s connection to acts of violence.

Recent surveys have found that in countries with high Muslim populations, the majority of Muslims have overwhelmingly negative views of terrorist groups like ISIS.

While Muslims aim to clear up misconceptions about their faith, the religion continues to spread rapidly. Today, Islam is the world’s fastest growing religion. Experts predict Islam will surpass Christianity as the largest religion by the end of the century.

Islam, BBC.
Islam Fast Facts, CNN.
Basic Facts About Islam, PBS.
What is Sharia Law and How is it Applied? BBC.
In nations with significant Muslim populations, much disdain for ISIS. Pew Research Center.
Islam Rituals and Worship: Symbolism, The Religion Library.
The Islamic Calendar: TimeandDate.com.
Sufism. The British Library.
What is Sufism?  The Threshold Society.
"Black Muslims account for a fifth of all U.S. Muslims, and about half are converts to Islam," by Besheer Mohamed and Jeff Diamant, January 17, 2019, Pew Research Center.