A coregency (or co-principality) is the situation where a monarchical position (such as king, queen, emperor or empress), normally held by only a single person, is held by two.

Historical examples of this include the coregency of Frederick I of Austria and Louis the Bavarian over the Kingdom of Germany, and the coregency of William and Mary over England (along with Wales), Scotland, and Ireland. It was also found in Sparta with two Kings, San Marino with two Captains Regent, the ancient Roman Empire (by determination of Hadrian) and the Byzantine Empire, Ancient Egypt and Nubia, in these cases as a balance between King and Queen, male and female. 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.).

The city of Maastricht was under the joint jurisdiction (parage) of the duke of Brabant and the prince-bishop of Liège. In 1648 it became a real condominium of two independent states, the Principality of Liège and the republic of the United Provinces. The coregency of the last was no longer held by a person but by the Estates-General of the Netherlands (until 1794).