The Imam must rise and rule as a qualified descendant of Ali

Zaydi Shia affirm that the rightful Imam must be a learned and pious descendant of Ali and Fatima, through either Hasan or Husayn, who publicly claims the office and rises in arms to establish just rule. Unlike the Twelver and Ismaili lines, which pass the imamate by explicit designation from father to son, Zaydism makes the office contingent on a qualified claimant actually asserting it, so that the imamate can lapse when no one rises and be revived when one does.

The Yemeni Zaydi imamate proper was founded in 897 CE by al-Hadi ila'l-Haqq Yahya, who established his rule at Sada in the northern highlands and whose teaching developed into the Hadawi school of law that Zaydis follow; in jurisprudence this school stands closer in method to Sunni fiqh, drawing on reasoning and analogy in ways the Twelver Shia legal tradition, built instead around the rulings of the Twelve Imams, does not.

The Zaydi imamate in Yemen endured, with interruptions, for over a thousand years until the republican revolution of 1962 overthrew the last ruling imam, Muhammad al-Badr, an event that ended Zaydi imamate rule as a state even as Zaydi religious identity and the Hadawi legal tradition continued, including within the modern Houthi movement, which has drawn on Zaydi revivalist ideas since the 1990s.

This activist conception, named for Zayd ibn Ali who rebelled and was killed in 740, produced a tradition that accepts that a less excellent leader may in fact rule while the more excellent is passed over, a concession that brings Zaydism closer to Sunni positions than the other Shia branches. Zaydi imams governed highland Yemen for over a thousand years. The belief expresses a Shia loyalty to the family of the Prophet fused with a demand that authority be earned by knowledge and courage rather than merely inherited.

In recent decades some Zaydi religious currents, particularly the Believing Youth movement founded by Hussein al-Houthi in the 1990s and the Houthi movement it gave rise to, have moved doctrinally and ritually closer to Twelver Shiism, adopting elements of Twelver commemoration and rhetoric that traditional Zaydi scholars regard as a departure from the historic Zaydi and Hadawi position; other Zaydi communities and scholars, especially those associated with the older Sada religious establishment, have resisted this shift and maintained the tradition's distinctive closeness to Sunni legal method. The tension illustrates that even a centuries-old school with settled doctrine continues to be reshaped by contemporary political and religious movements claiming its name.