The majority of Muslims in Iran are Shiites, which is a branch of Islam that follows the teachings of the Prophet Muhammad's son-in-law, Ali. Shiites make up around 90% of the population in Iran and are the largest religious group in the country. They are also the majority in Iraq, Bahrain, and Azerbaijan. Shiites have their own set of beliefs and practices that differ from those of other branches of Islam, such as Sunnis.