Imāmah (Arabic: اٍمامة‎) means “leadership” and it is a part of the Shi'a theology. The Twelve Imams are the spiritual and political successors to Muhammad, the Prophet of Islam, in the Twelver or Ithna Ashariya branch of Shia Islam. According to the theology of Twelvers, the successor of Muhammad is an infallible human individual who not only rules over the community with justice, but also is able to keep and interpret the Divine Law and its esoteric meaning. The Prophet and Imams’ words and deeds are a guide and model for the community to follow; as a result, they must be free from error and sin, and must be chosen by divine decree, or nass, through the Prophet.

It is believed in Shi'a Islam that Aql, a divine wisdom, was the source of the souls of the Prophets and Imams and gave them esoteric knowledge, called Hikmah, and that their sufferings were a means of divine grace to their devotees. Although the Imam was not the recipient of a divine revelation, but has close relationship with God, through which God guides him, and the imam in turn guides the people. The Imamat, or belief in the divine guide, is a fundamental belief in Shi'i Islam and is based on the concept that God would not leave humanity without access to divine guidance.

Twelver or Imami Shīa Islam (Athnā‘ashariyyah or Ithnā‘ashariyyah, Arabic: اثنا عشرية‎) is the largest branch of Shī‘ī (Shi'a) Islam. Adherents of Twelver Shī‘ism are commonly referred to as Twelvers, which is derived from their belief in twelve divinely ordained leaders, known as the Twelve Imāms and their belief that the Mahdi will be none other than the returned Twelfth Imam that disappeared and is believed by Twelvers to be in occultation. Approximately 85% of Shī‘a are Twelvers, and the term Shi'a Muslim as commonly used in English usually refers to Twelver Shī‘a Muslims only.

Twelvers share many tenets of Shī‘ism with related sects, such as the belief in Imāms, but the Ismā‘īlī and Zaydī Shī‘ī sects each believe in a different number of Imāms and for the most part, a different path of succession regarding the Imāmate. They also differ in the role and overall definition of an Imām.

The Twelver faith is a majority in countries like Iran, Iraq, Azerbaijan, Bahrain, and Lebanon. Alevis in Turkey and Albania and Alawis of Syria also regard themselves as Twelvers, but hold significantly different beliefs from mainstream Twelver Shiites. The Twelver faith also forms a large minority in India,Pakistan, Afghanistan, Nigeria, Tanzania, Kuwait, Qatar, UAE and Saudi Arabia. Smaller minorities of Twelver also exist in Oman, Yemen, Egypt, Sudan, Kenya, Ghana, Senegal, Indonesia, Malaysia and in many other countries of the world, including Europe and the Americas.

Shia Islam (Arabic: شيعة‎, Shīʿah) is the second largest denomination of Islam. Adherents of Shia Islam are called Shi'as, Shi'ites, or Shias. "Shia" is the short form of the historic phrase Shīʻatu ʻAlī (شيعة علي), meaning "followers of Ali", "faction of Ali", or "party of Ali".

Like other schools of thought in Islam, Shia Islam is based on the teachings of the Quran and the message of the Islamic prophet Muhammad. In contrast to other schools of thought, the Shia believe that only God has the right to choose a representative to safeguard Islam, the Quran and sharia (based upon verses in the Quran which stipulate this according to the Shia). For this reason, the Shias look to Ali, whom they consider divinely appointed, as the rightful successor to Muhammad, and the first imam. The Shia believe that there are numerous narrations where Muhammad selected Ali as his successor.

Shias believe that Muhammad's family, the Ahl al-Bayt ("the People of the House"), and certain individuals among his descendants, who are known as Imams, have special spiritual and political authority over the community. Therefore, Shias prefer hadith attributed to the Ahl al-Bayt and close associates, and have their own separate collection of hadiths. All Shias agree on the succession of Hassan and Hussein after Ali, but they may differ after Hussein. Hassan and Hussein are described by Shias as "leaders of all youths in Paradise", and believe that these sons of Ali were the true leaders and caliphs of the Muslims. Shias regard Ali as the successor of Muhammad not only ruling over the community in justice, but also interpreting Islamic practices and its esoteric meaning. Hence he was regarded as being free from error and sin (infallible), and appointed by God by divine decree (nass) to be the first Imam. Ali is known as "perfect man" (al-insan al-kamil) similar to Muhammad, according to Shia viewpoint.

Shi or shi may refer to:

Doctrine (from Latin: doctrina) is a codification of beliefs or a body of teachings or instructions, taught principles or positions, as the body of teachings in a branch of knowledge or belief system. The Greek analogue is the etymology of catechism.

Often doctrine specifically connotes a corpus of religious dogma as it is promulgated by a church, but not necessarily: doctrine is also used to refer to a principle of law, in the common law traditions, established through a history of past decisions, such as the doctrine of self-defense, or the principle of fair use, or the more narrowly applicable first-sale doctrine. In some organizations, doctrine is simply defined as "that which is taught", in other words the basis for institutional teaching of its personnel internal ways of doing business.

Examples of religious doctrines include:

One department of the Roman Curia is called the Congregation for the Doctrine of the Faith. Also shows other doctrines involved in the shape of government and politics.