Abūʾl-Faḍl Muḥammad ibn Ḥusayn Bayhaqī (Persian: ابوالفضل محمد بن حسین بیهقی; died September 21, 1077), better known as Abu'l-Faḍl Bayhaqi (ابوالفضل بیهقی; also spelled Beyhaqi), was a Persian secretary, historian and author.

Educated in the major cultural center of Nishapur, and employed at the court of the famous Ghaznavid Sultan Mahmud, Bayhaqi was a highly cultured man, whose magnum opus—the Tarikh-i Bayhaqi, is seen as the most reliable source of valid information about the Ghaznavid era, which was written in an exquisite and vivid Persian prose that would become an ideal model for several eras.

Bayhaqi is praised by modern scholars for his frankness, precision, and elegant style in his book, which he had spent 22 years to write, finishing it in thirty volumes, of which however only five volumes and half of the sixth exist today. Julie Scott Meisami places Bayhaqi among the historians of the Islamic Golden Age.