After Manzikert, a partial recovery (referred to as the Komnenian restoration) was made possible by the Komnenian dynasty. The first Komnenian emperor was Isaac I (1057–1059), after which the Doukas dynasty held power (1059–81). The Komnenoi attained power again under Alexios I in 1081. From the outset of his reign, Alexios faced a formidable attack by the Normans under Robert Guiscard and his son Bohemund of Taranto, who captured Dyrrhachium and Corfu, and laid siege to Larissa in Thessaly. Robert Guiscard's death in 1085 temporarily eased the Norman problem. The following year, the Seljuq sultan died, and the sultanate was split by internal rivalries. By his own efforts, Alexios defeated the Pechenegs; they were caught by surprise and annihilated at the Battle of Levounion on 28 April 1091.

Having achieved stability in the West, Alexios could turn his attention to the severe economic difficulties and the disintegration of the Empire's traditional defences. However, he still did not have enough manpower to recover the lost territories in Asia Minor and to advance against the Seljuks. At the Council of Piacenza in 1095, envoys from Alexios spoke to Pope Urban II about the suffering of the Christians of the East, and underscored that without help from the West they would continue to suffer under Muslim rule.

The brief first coinage of the Thessaloniki mint, opened by Alexios in September 1081, on his way to confront the invading Normans under Robert Guiscard

Urban saw Alexios' request as a dual opportunity to cement Western Europe and reunite the Eastern Orthodox Church with the Roman Catholic Church under his rule. On 27 November 1095, Pope Urban II called together the Council of Clermont, and urged all those present to take up arms under the sign of the Cross and launch an armed pilgrimage to recover Jerusalem and the East from the Muslims. The response in Western Europe was overwhelming.

Alexios had anticipated help in the form of mercenary forces from the West, but he was totally unprepared for the immense and undisciplined force that soon arrived in Byzantine territory. It was no comfort to Alexios to learn that four of the eight leaders of the main body of the Crusade were Normans, among them Bohemund. Since the crusade had to pass through Constantinople, however, the Emperor had some control over it. He required its leaders to swear to restore to the empire any towns or territories they might conquer from the Turks on their way to the Holy Land. In return, he gave them guides and a military escort.

Alexios was able to recover a number of important cities and islands, and in fact much of western Asia Minor. Nevertheless, the Catholic/Latin crusaders believed their oaths were invalidated when Alexios did not help them during the siege of Antioch (he had in fact set out on the road to Antioch but had been persuaded to turn back by Stephen of Blois, who assured him that all was lost and that the expedition had already failed). Bohemund, who had set himself up as Prince of Antioch, briefly went to war with the Byzantines, but he agreed to become Alexios' vassal under the Treaty of Devol in 1108, which marked the end of the Norman threat during Alexios' reign.