The Husaynids (Arabic: بنو الحسين, romanized:Banū al-Ḥusayn or حسینیون, Ḥusayniyyūn) are a branch of the Alids who are descendants of Husayn ibn Ali, a grandson of the Islamic prophet Muhammad. It is one of the two main branches of the ashrāf (the other being the descendants of Husyan's brother Hasan, the Hasanids).
the various lines of Shi'a imams are largely Husaynid, being descended patrilineally from Husayn ibn Ali, the third imam. This applies to the Twelver Shi'a imams, the Zaydiyya, and the various lines of Isma'ili imams.