By the 11th century, Byzantine aristocrats had ceased to hold any significant power, clinging instead to the honorific titles they held by virtue of being related to the ruling emperor. These were often used to bid for power within the government, sometimes at as high a level as the throne itself. By the reign of Constantine IX in the middle part of the century they had also begun to assert sovereignty over various parts of the empire, collecting taxes for themselves and often plotting rebellions against the emperor.
In the late 11th century Alexius I attempted to reform the aristocracy, taking the pacifying measure of distributing Byzantine territory amongst its members. Doing so had the added benefit of removing them from Constantinople, making it harder for them to directly challenge the emperor's authority. Most pronoiai granted by Alexius, however, were to members of his own (Comnenus) family. Alexius simply legitimized the holding of land by aristocrats, and brought it under centralized state control.
Alexius' grandson Manuel I Comnenus continued to grant land to the aristocrats, but also extended pronoiai to aristocratic officers in the army, in place of giving them a regular salary. Pronoiai developed into essentially a license to tax the citizens who lived within the boundaries of the grant (the paroikoi). Pronoiars (those who had been granted a pronoia) became something like tax collectors, who were allowed to keep some of the revenue they collected. This idea was not completely new; centuries before, Heraclius had reorganized the empire's land into military districts called Thema. Under this system, military officers (strategoi) ran each district and collected rent from the peasants who farmed the land. However, the paroikoi, under either the Thema or pronoia system, were not serfs as peasants were in the feudal system of western Europe. They owed no particular loyalty or service to the strategos or pronoiar, as in both cases the emperor was still the legal owner of the land. The pronoiar was most likely not even a native of the land he had been granted.
The size and value of the pronoia, the number of paroikoi, and the duties owed by them were recorded in praktika. A pronoiar would likely be able to collect trade revenue and part of the crop harvested on the land, and could also hold hunting rights and transportation rights. A praktika also recorded the duties owed by the pronoiar to the emperor. If necessary, the emperor could request military service, although the pronoiar could not force his taxpayers to join him. Pronoiars were often reluctant to give military service if he lived a prosperous life on his grant, and they had some autonomy if they chose not to serve. If they could gain the support of their taxpayers, they could lead rebellions against the empire, but these were not as dangerous as rebellions in the capital, which Alexius' system could now more successfully avoid. Neither Alexius, Manuel, or the other 12th century emperors seemed to worry about provincial rebellions, seemingly assuming that a pronoia grant would eventually appease a rebellious noble. During the Fourth Crusade, Alexius IV still thought this way, and granted Crete to Boniface of Montferrat, under the assumption that the Crusaders would go away if their leader had some land.
After the Crusaders captured Constantinople in 1204, the pronoia system continued in the Empire of Nicaea, where the emperors ruled in exile. John III Ducas Vatatzes also gave pronoiai to the church and noblewomen, which had not been done before. When Constantinople was recaptured by Michael VIII Palaeologus in 1261, he allowed pronoiai to be inherited, which made the empire more like the feudal states in Europe. He also audited the pronoiai to make their values more realistic according to contemporary conditions, as the empire had lost much of its land and revenue since the 11th century. Under the Palaeologans, pronoiars could more easily be organized into military units if the emperor required their service. The emperor could also confiscate the revenues for whatever reason. Andronicus II Palaeologus, for example, used the money raised by the pronoiars to finance military expeditions against the Bulgarians, but he did not require them to provide military service themselves. During this time pronoiars could also attract followers by giving them pronoia grants of their own.
Recruiting pronoiars to form an army helped unite the remnants of the empire after 1261. However, there were by this time only a few thousand pronoiars, and although they paid for their own expenses, the emperors could not afford a full army or navy to strengthen the empire's defenses. The impoverished empire had very little tax revenue, and pronoiars began to extract rents from the paroikoi, turning back to the old Thema system.
The empire continued to lose land to the Ottoman Empire, and Constantinople was finally lost in 1453, but the Ottomans continued to use their own version of the pronoia system, which they had borrowed from the Byzantines during their conquests.