Heresy

thumb|Saint Nicholas with [[Arius at the Council of Nicaea, at which he is said to have hit him; Arius was known for preaching that Jesus was created by God and has a lower status, a heresy in Trinitarian Christianity]]Heresy is any belief or theory that is strongly at variance with established beliefs or customs, particularly the accepted beliefs or religious law of a religious organization. A heretic is a proponent of heresy.

In Islam and sharia (Islamic law), '''' ( , ) refers to innovation in religious matters. The category is further divided into bid'ah al-ibadat and bi'da al-mu'amalat''. The first category refers to innovations in sacred matters, such as worship, and are generally forbidden as it violates the textual source of the Quran and the Sunnah. The second refers to innovations in the mundane realm and is often permissible, as long as it does not violate the Sharia.

Zurvanism was a fatalistic religious movement of Zoroastrianism in which the divinity Zurvan is a first principle (primordial creator deity) who engendered equal-but-opposite twins, Ahura Mazda and Angra Mainyu. Zurvanism is also known as "Zurvanite Zoroastrianism", and may be contrasted with Mazdaism.

Atenism, also known as the Aten religion, the Amarna religion, and the Amarna heresy, was a religion in ancient Egypt. It was founded by Akhenaten, a pharaoh who ruled the New Kingdom under the Eighteenth Dynasty. The religion is described as monotheistic or monolatristic, although some Egyptologists argue that it was actually henotheistic. Atenism was centered on the cult of Aten, a god depicted as the disc of the Sun. Aten was originally an aspect of Ra, Egypt's traditional solar deity, though he was later asserted by Akhenaten as being the supreme of all deities.

Zindīq (pl. zanādiqa) is an Islamic pejorative applied to individuals who are considered to hold views or follow practices that are contrary to central Islamic dogma. Zandaqa is the noun describing these views.

In theology or the history of religion, heresiology is the study of heresy, and heresiographies are writings about the topic. Heresiographical works were common in both medieval Christianity and Islam.