Бір мемлекетте бірнеше билеушінің болуы

Situation in a single person monarchy in which two or more people hold the title
multiple sovereigns of a single state

A coregency is the situation where a monarchical position (such as prince, princess, king, queen, emperor or empress), normally held by only a single person, is held by two or more. It is to be distinguished from diarchies or duumvirates such as ancient Sparta and Rome along with a regency where the monarch in most cases infant or incapacitated particularly has a senior above him and exercises no power whatsoever apart from legally holding the position of head of state.

Co principality is a distinct but related system employed in contemporary Andorra, where monarchical power is formally divided between two rulers.

Coregencies were common in the Hellenistic period; according to one scholar, they "can usually be explained as a means of avoiding crises of succession or internal conflict, and of strengthening dynastic identity and ideology." Other examples include the coregency of Frederick I of Austria and Louis the Bavarian over the Kingdom of Germany. Jure uxoris Kings in Kingdoms such as Spain and Portugal can also be found (Ferdinand V and Isabella I of Castile, Philip I and Joanna of Castile, Peter III and Maria I of Portugal, etc.). In Navarre, the husbands of queens regnant were styled as co rulers.

In Ancient Egypt, coregency was quite problematic as the Pharaoh was seen as the incarnation/representation of the god Horus. Therefore, according to the divine order Ma'at, only one King could exist at the same time. Yet, exceptions can be found, mainly in the Middle Kingdom, where the pharaoh occasionally appointed his successor (often one of his sons) as coregent, or joint king, to ensure a smooth succession. “This system was used, from at least as early as the Middle Kingdom, in order to ensure that the transfer of power took place with the minimum of disruption and instability”. Coregencies are highly probable for Amenemhat I > Senusret I > Amenemhat II > Senusret II. Most probably the real king in power was the older one (father) adopting the younger ruler (son), while the co regent had to wait until after the death of the older one to really have access to full royal power. Yet, the years of reigns normally were counted from the beginning of the coregency on. Due to this and to the fragmentary character of known sources, the establishment of Egyptian chronology was quite complicated and remains disputed up to date. Yet, understanding the existence of co regency reduced the chaos quite a lot. The institution of coregency is different from that of vice regency, where an adult person (in Ancient Egypt often the mother of the king) functions as Legal guardian, ruling in the name of the underage king. Some of the female vice regents of Egypt rose to a status of equal to the God Kings, becoming co rulers as can be seen in the famous case of Hatshepsut. After the death of her husband Thutmose II, Hatshepsut ruled in the name of Thutmose III, her nephew and stepson. Then, latest in year 7 of Thutmose III's reign, she took over royal regalia and was then titled King of Egypt under the Throne name (prenomen) Maatkare. For later periods of Pharaonic Egyptian history, the existence of the institution of coregency has been put into question by Egyptologists, while, "the Ptolemaic and Roman period examples being the most securely identified". As such, when Hugh died it did not trigger an election for a new king, nor did Robert necessarily "inherit" the crown, but simply continued his kingship. Subsequent Capetian kings would also name their eldest son or brother as co ruler, until the tradition of agnatic primogeniture was sufficiently established to transform the King of France from an elected monarch to a hereditary one.

It was common during the Principate for a Roman emperor or Augustus to appoint Caesar as designated heir and junior co emperor, in many cases adopting them as their son, who did not necessarily have to be biologically related to them. This was merely a tradition and not a formal office until the Tetrarchy, which attempted to codify this arrangement, but quickly fell apart. It regained significance, including under Zeno, as well as when Justin I had his nephew Justinian named co emperor shortly before his own death, Constantine IV was also named co emperor by his father Constans II and who himself had several other co emperors, and the practice was common in the centuries to come up through the Palaiologans.

Following the death of Tsar Feodor III of Russia in 1682, his brother Ivan and half brother Peter were both crowned autocrats of Russia. This compromise was necessary because Ivan was unfit to rule due to physical and mental disabilities, while Peter's exclusive rule was opposed by Feodor and Ivan's older sister Sofia Alekseyevna, who led a Streltsy uprising against him and his mother's family. Because neither Tsar was of age to rule, Sofia subsequently claimed regency until she was removed from power by Peter in 1689. Ivan V and Peter I's joint reign continued, however, with Ivan maintaining formal seniority despite having little participation in the affairs of the state until his death in 1696, at which point Peter became the sole ruler.

The monarchy in Sweden has had several periods of joint rule: Erik and Alrik, Yngvi and Alf, Björn at Hauge and Anund Uppsale, Eric the Victorious and Olof Björnsson, Eric the Victorious and Olof Skötkonung, Halsten Stenkilsson and Inge I, and Philip and Inge II.

Coregency is a special feature of the Trần dynasty, in which a senior king abdicated in favor of his chosen heir. This abdication, however, is only in name, as the abdicated king continued to rule while his successor sat on the throne as a learner.