Bahshamiyya (Arabic: البهشمية, also known as "Ba Hashimiyya") was a Mu'tazili-influenced school of thought, rivaling the school of Abd al-Jabbar ibn Ahmad, based primarily on the earlier teaching of Abu Hashim al-Jubba'i, the son of Abu 'Ali Muhammad al-Jubba'i.

Mu'tazila is a school of rationalist Islamic theology known as Kalam. Early practitioners stressed the supremacy of human reason and free-will (similar to Qadariyya) and went on to develop an epistemology, ontology and psychology which provide a basis for explaining the nature of the world, God, man and religion. According to Mu'tazilis, good and evil are easily reconciled through human reason without esoteric methods.

The Mu'tazila school started in the 8th century; its iterative refinement continued from the late 10th century until mid-11th century CE. Mu'tazila was briefly the official theology of the Abbasid caliphs in the 9th century. The impact of Mu'tazila doctrine continues to be felt in primarily three groups: Shi'a (Ismai'li) Islam, Karaite Judaism, and to a much lesser extent Rabbanite Judaism of the Sephardic Rite and Yemenite rite.

By the end of the 9th century Mu'tazila had split into two schools:

The Basra school was led by Abū 'Alī al-Jubbā'ī and his son Abū Hāshim. Students and followers of Abû Hâshim formed a sub-school known as the Bahshamiyya. The most noteworthy practitioners were:

1. Abū 'Alī ibn Khallād

2. Abū 'Abd Allāh al-Basrī

3. Abū Ishāq ibn 'Ayyāsh