A dynasty is a sequence of rulers from the same family, usually in the context of a monarchical system, but sometimes also appearing in republics. A dynasty may also be referred to as a "house", "family" or "clan", among others.

Historians periodize the histories of many states and civilizations, such as the Roman Empire (27 BC – AD 1453), Imperial Iran (678 BC – AD 1979), Ancient Egypt (3100–30 BC), and Ancient and Imperial China (2070 BC – AD 1912), using a framework of successive dynasties. As such, the term "dynasty" may be used to delimit the era during which a family reigned.

Before the 18th century, most dynasties throughout the world were traditionally reckoned patrilineally, such as those that followed the Frankish Salic law. In polities where it was permitted, succession through a daughter usually established a new dynasty in her husband's family name. This has changed in all of Europe's remaining monarchies, where succession law and conventions have maintained dynastic names de jure through a female.

The word "dynasty" (from the Greek: δυναστεία, dynasteía "power", "lordship", from dynástes "ruler") is sometimes used informally for people who are not rulers but are, for example, members of a family with influence and power in other areas, such as a series of successive owners of a major company, or any family with a legacy, such as a dynasty of poets or actors. It is also extended to unrelated people, such as major poets of the same school or various rosters of a single sports team.

The dynastic family or lineage may be known as a "noble house", which may be styled as "imperial", "royal", "princely", "ducal", "comital" or "baronial", depending upon the chief or present title borne by its members, but it is more often referred by adding the name afterwards, as in "House of Habsburg".

A ruler from a dynasty is sometimes referred to as a "dynast", but this term is also used to describe any member of a reigning family who retains a right to succeed to a throne. For example, King Edward VIII ceased to be a dynast of the House of Windsor following his abdication.

In historical and monarchist references to formerly reigning families, a "dynast" is a family member who would have had succession rights, were the monarchy's rules still in force. For example, after the 1914 assassinations of Archduke Franz Ferdinand of Austria and his morganatic wife, their son Maximilian, Duke of Hohenberg, was bypassed for the Austro-Hungarian throne because he was not a Habsburg dynast. Even after the abolition of the Austrian monarchy, Duke Maximilian and his descendants have not been considered the rightful pretenders by Austrian monarchists, nor have they claimed that position.

The term "dynast" is sometimes used only to refer to agnatic descendants of a realm's monarchs, and sometimes to include those who hold succession rights through cognatic royal descent. The term can therefore describe overlapping but distinct sets of people. For example, David Armstrong-Jones, 2nd Earl of Snowdon, a nephew of Queen Elizabeth II, is in the line of succession to the British crown, making him a British dynast. On the other hand, since he is not a patrilineal member of the British royal family, he is not a dynast of the House of Windsor.