political and religious dynasty that dominated an empire in North Africa and subsequently in the Middle East from AD 909 to 1171 and tried unsuccessfully to oust the ʿAbbāsid (Abbāsid Dynastyʿ) caliphs as leaders of the Islāmic world (Caliphate). It took its name from Fāṭimah, the daughter of the Prophet Muḥammad, from whom the Fāṭimids claimed descent.

Before the Fāṭimids, there had been other rulers in North Africa and Egypt who had succeeded in making themselves virtually independent of the ʿAbbāsid caliphs in Baghdad; but they had been Muslims of the Sunnī branch of Islām, willing to recognize the token suzerainty of the caliph as head of the Islāmic community. The Fāṭimids, however, were the heads of a rival religious movement—the Ismāʿīlī (Ismāʿīlīte) sect of the Shīʿī (Shīʿite) branch—and dedicated to the overthrow of the existing religious and political order in all Islām. Unlike their predecessors, they refused to offer even nominal recognition to the ʿAbbāsid caliphs, whom they rejected as usurpers. They themselves—as Ismāʿīlī imām (imam)s (spiritual leaders), descendants of the Prophet through his daughter Fāṭimah and his kinsman ʿAlī—were, in the eyes of their followers, the rightful caliphs, both by descent and by divine choice the custodians of the true faith and the legitimate heads of the universal Islāmic state and community. Their purpose was not to establish another regional sovereignty but to supersede the ʿAbbāsids and to found a new caliphate in their place.

During the 9th century, Ismāʿīlī missionaries became established in many parts of the Islāmic empire, preaching a doctrine of revolution against the Sunnī order and the ʿAbbāsid state. After a number of unsuccessful risings, the Ismāʿīlīs were able to establish a firm base in the Yemen; from there they sent emissaries to North Africa, where they achieved their greatest success. By 909 they were strong enough for their imām, who had been in hiding, to emerge and proclaim himself caliph, with the messianic title of al-Mahdī (the Divinely Guided One). This marked the beginning of a new state and dynasty.

For the first half-century the Fāṭimid caliphs ruled only in North Africa and Sicily, where they had to deal with many problems. Most of their subjects were Sunnīs of the Mālikī school; others—a substantial minority—were the Khawārij, or Khārijites. Neither group was well disposed toward the Ismāʿīlī doctrines of the new rulers, and they offered stubborn resistance to them. Even among the Ismāʿīlīs themselves, a conflict soon arose between the state and the revolution—that is, between the caliph al-Mahdī (reigned 909–934) and the missionaries who had brought him to power. There also were political problems with Berber tribes and neighbouring Muslim rulers, as well as a war against the Byzantines in Sicily and Italy that the Fāṭimid rulers had inherited from their North African predecessors.

While coping with these difficulties, the Fāṭimids never lost sight of their ultimate aim, expansion to the East, where the centre of ʿAbbāsid strength lay. The first step was the conquest of Egypt (Egypt, ancient). The first caliph, al-Mahdī, established his capital at Mahdīyah (founded 920) on the east coast of Tunisia. His successors al-Qāʾim (reigned 934–946), al-Manṣūr (reigned 946–953), and al-Muʿizz (Muʿizz, al-) (reigned 953–975) ruled from there. In 913–915, 919–921, and 925 unsuccessful expeditions were sent against Egypt. Finally, in 969, under the caliph al-Muʿizz, the first stage in the advance to the East was completed. Fāṭimid troops conquered the Nile Valley and advanced across Sinai into Palestine and southern Syria. Near al-Fusṭāt, the old administrative centre of Muslim Egypt, the Fāṭimids built Cairo, which became the capital of their empire, and in it a new cathedral mosque and seminary, called al-Azhar, after Fāṭimah az-Zahrāʾ (the Resplendent), the ancestress of the dynasty.

For more than a century the Fāṭimid rulers in Cairo pursued their aim of establishing the universal Ismāʿīlī imamate. At times they were compelled by other problems—war on the frontiers, trouble in the Mediterranean, unrest at home or in the provinces—to reach some agreement with their Sunnī rivals; but such arrangements were always temporary.

The Fāṭimid caliphate was a regime at once imperial and revolutionary. At home, the caliph was a sovereign, governing a vast empire and seeking to expand it by normal military and political means. Its heart was Egypt; its provinces at its peak included North Africa, Sicily, the Red Sea coast of Africa, Syria, Palestine, the Yemen, and the Hejaz, with the two holy cities of Mecca and Medina. Control of these was of immense value to a Muslim ruler, conferring great religious prestige and enabling him to exploit the annual pilgrimage to his advantage.

The caliph was not only an emperor; he was also an imam—the spiritual head of the Ismāʿīlīs wherever they were and, according to Ismāʿīlī doctrine, the embodiment of God's infallible guidance to mankind. As such he was the archenemy of the Sunnī ʿAbbāsid order and the hope and refuge of those who wished to overthrow it. In all the lands still under ʿAbbāsid suzerainty, he commanded a great network of missionaries and agents, and he used them to gain converts for the Ismāʿīlī faith and workers for the Fāṭimid cause; their task was also to preach and, where possible, to practice subversion against the Sunnī order and the regimes that supported it. The mission was elaborately and secretly organized under the supreme direction of the chief missionary in Cairo. In the Fāṭimid state the mission became in effect a third branch of the government, together with the traditional military and bureaucratic establishments; it thus approximated to something otherwise lacking in the medieval Islāmic world—an institutionalized state church.

The primary tasks of the mission were the formulation and dissemination of Ismāʿīlī doctrine. Ismāʿīlī theology supplied the arguments by which the Fāṭimids denied the ʿAbbāsid claim to the caliphate and asserted their own, and was thus a powerful weapon in their armoury. First in Tunisia and then in Egypt, a series of distinguished theologians wrote what became the classical formulations of Ismāʿīlī doctrine. The Fāṭimids also founded great libraries and colleges, whose functions were to train missionaries to go out into the field, and to provide further instruction for the converts sent to Cairo for this purpose.

The work of the mission was only a part—albeit an important one—of the Fāṭimid grand strategy against the Sunnī Empire; in this strategy, the universal aims of the Ismāʿīlī faith and the imperial purposes of the Fāṭimid state met and merged. Linked with these actions was a great commercial expansion and an economic policy aimed at developing the Red Sea trade between Asia and the Near East, to the detriment of the alternative route through the Persian Gulf, which was controlled by the Sunnī powers. In the course of this effort, the Fāṭimids extended their rule down both shores of the Red Sea, established their supremacy in Yemen, and sent missionaries to eastern Arabia, to Central Asia, and to India.

The height of Fāṭimid expansion to the East was reached in 1057–59, when a dissident general in Iraq changed sides and proclaimed the Fāṭimid caliph in Mosul and then, for a year, in Baghdad itself. The Fāṭimids were unable to provide support, however, and the general was driven out of Baghdad by the Seljuq Turks. This proved to be a turning point and the beginning of the decline of both Fāṭimid power and Ismāʿīlī influence.

Several reasons may be adduced for the failure of the Fāṭimid bid for Islāmic leadership. One was their adoption and retention of a religious doctrine that was ultimately unacceptable to the Sunnī majority. Fāṭimid Ismāʿīlism, as a theology, was remote from the central consensus of Islām, and with the Sunnī revival of the 11th and 12th centuries its rejection became certain. The coming of the crusaders indirectly sealed its fate, for in the great 12th-century contest between Islām and Christendom there was no room for dissention on the Muslim side.

In their ventures abroad, the Fāṭimids achieved many successes, the most notable being the conquest of Egypt itself. They suffered repeated setbacks, however, in Palestine and Syria where, in addition to local opponents, they also had to face major attacks from outside—by the Byzantines, the Turks, and then the European crusaders. It was in Syria that the great Fāṭimid advance to the East was delayed and halted; and it was in Syria that a new power arose that in time destroyed them.

These troubles abroad no doubt fed, and were fed by, the growing discontents in Egypt. At first the caliphs retained full personal control of affairs, presiding over an essentially civilian government. The army's importance increased, however, and factional differences arose among the Berber, Turkish, Sudanese, and Nubian troops. Fights between the different groups first became a factor during the reign of al-Ḥākim (Ḥākim, al-) (reigned 996–1021), in whose time, partly because of his own highly eccentric behaviour, the personal authority and religious prestige of the caliph began to decline. His successors became little more than puppets in the hands of their viziers and their generals. During the long reign of al-Mustanṣir (Mustanṣir, al-) (reigned 1036–94) factional strife brought Egypt into a vicious circle of anarchy and tyranny, made worse by recurring famine and plague. The provinces, in east and west, were lost to local dynasts or invaders.

In 1073, an able soldier, Badr al-Jamālī, went to Cairo at the invitation of the caliph and seized power; in one night his officers rounded up the leading generals and officials and put them to death. He assumed the titles of commander of the armies, director of the missionaries, and vizier, symbolizing his control of the military, religious, and bureaucratic establishments; it is by the military title that he is usually known. Badr al-Jamālī restored order and, for a while, even brought some measure of prosperity. Egypt came under the rule of a military regime, headed by the commander of armies and maintained by his troops. The office became permanent; Badr was succeeded by his son and then by a series of military autocrats who kept the Fāṭimid caliphs in tutelage. The later commanders were not even Ismāʿīlīs.

Badr and his successors saved the Fāṭimid state from collapse and postponed its end for nearly a century. Responding to the Seljuq challenge from the East, he pursued an active policy in Syria, Arabia, and elsewhere, using both religious and worldly weapons. In Syria, however, the armies of the Fāṭimids suffered repeated defeats; in Arabia their following was reduced to insignificance. Badr's son and successor al-Afḍal in effect renounced the claims of the Egyptian Fāṭimid dynasty to the universal caliphate.

On the death of al-Mustanṣir in 1094 it was al-Afḍal who chose the new caliph. Al-Mustanṣir had nominated his elder son, Nizār, who had been accepted by the Ismāʿīlī leaders; the younger son, Aḥmad, was a youth without allies, who would be entirely dependent on his sponsor. It was no doubt with this in mind that al-Afḍal married his sister to Aḥmad and, on al-Mustanṣir's death, proclaimed his brother-in-law as caliph with the regnal name al-Mustaʿlī (reigned 1094–1101); in doing so, al-Afḍal split the sect from top to bottom.

Even in Egypt there was some opposition; in Persia, Iraq, and Central Asia the Ismāʿīlī mission, led by Ḥasan-e Ṣabbāḥ, refused to recognize the new caliph and broke off relations with the Fāṭimid authorities in Cairo. Ḥasan-e Ṣabbāḥ's new Ismāʿīlī movement, known after its Syrian branch as the Assassins (Assassin), proclaimed Nizār and his descendants as rightful imāms and condemned the caliphs in Cairo as usurpers. Even those Ismāʿīlīs, chiefly in the Yemen, who had accepted al-Mustaʿlī broke away in 1130 when al-Mustaʿlī's son al-Āmir (reigned 1101–30) was murdered by the Assassins and was succeeded by his cousin al-Ḥāfiẓ (reigned 1130–49). Claiming that al-Āmir had left an infant son who was now the hidden imām, the Yemenites refused to recognize al-Ḥāfiẓ or his successors in Cairo.

The end of the dynasty came in 1171. The last four caliphs were no more than a local Egyptian dynasty, without power, influence, or hope. In 1171, the last caliph died. Saladin, the nominal vizier, had become the real master of Egypt, and the Fāṭimid caliphate, already dead as a religious and political force, was formally abolished.