A prince regent or princess regent is a prince or princess who, due to their position in the line of succession, rules a monarchy as regent in the stead of a monarch, e.g., as a result of the sovereign's incapacity or absence.

In a monarchy, a regent is a person appointed to govern a state pro tempore because the actual monarch is a minor, absent, incapacitated or unable to discharge their powers and duties, or the throne is vacant and a new monarch has not yet been determined. One variation is in the Monarchy of Liechtenstein, where the competent Prince may choose to assign regency to their of-age heir, handing over the majority of their responsibilities to prepare the heir for succession. The rule of a regent or regents is called a regency. A regent or regency council may be formed ad hoc or in accordance with a constitutional rule. Regent is sometimes a formal title granted to a monarch's most trusted advisor or personal assistant. If the regent is holding the position due to their being in the line of succession, the compound term prince regent is often used; if the regent of a minor is their mother, and she is wife or widow of the king, she would be referred to as queen regent.