Until the 19th century, it was taken for granted that a legitimate function of a monarch was to aggrandize his dynasty: that is, to increase the territory, wealth, and power of his family members. The longest-surviving dynasty in the world is the Imperial House of Japan, the Yamato dynasty, whose reign is traditionally dated to 660 BC.
Prior to the 20th century, dynasties throughout the world have traditionally been reckoned patrilineally, such as under the Frankish Salic law.In nations where it was permitted, succession through a daughter usually established a new dynasty in her husband's ruling house. This has changed in some places in Europe, where succession law and convention have maintained dynasties through a female, for example the House of Windsor is maintained through the children of Queen Elizabeth II, similarly with the Monarchy of the Netherlands whose dynasty remained the House of Orange-Nassau through three successive queens regnant. The earliest such example among the major European monarchies was in Russia in the 18th century, where the name of the House of Romanov was maintained through a non-ruling female.
Some states in Africa (Balobedu), determined descent matrilineally, while rulers have at other times adopted the name of their mother's dynasty when coming into her inheritance.
Less frequently, a monarchy has alternated or been rotated, in a multidynastic (or polydynastic) system that is, the most senior living members of parallel dynasties, at any point in time, constitute the line of succession.
The word "dynasty" is sometimes used informally for people who are not rulers but, for example, members of a family with influence and power in other areas, such as a series of successive owners of a major company. It is also extended to unrelated people such as major poets of the same school or various rosters of a single sports team.
The word "dynasty" derives from Latin dynastia from Greek dynastia (), where it referred to "power", "dominion", and "rule" itself. It was the abstract noun of dynsts (), the agent noun of dynamis (), "power" or "ability", from dnamai (), "to be able".
A ruler in 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, following his abdication, Edward VIII of the United Kingdom ceased to be a dynastic member of the House of Windsor.
A "dynastic marriage" is one that complies with monarchical house law restrictions, so that the descendants are eligible to inherit the throne or other royal privileges. The marriage of Willem-Alexander, Prince of Orange, to Mxima Zorreguieta in 2002 was dynastic, for example, and their eldest child is expected to inherit the Dutch crown eventually. But the marriage of his younger brother Prince Friso to Mabel Wisse Smit in 2003 lacked government support and parliamentary approval. Thus Friso forfeited his place in the order of succession, lost his title as a Prince of the Netherlands, and left his children without dynastic rights.
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 Sophie von Hohenberg, their son Max was bypassed for the Austrian throne because he was not a Habsburg dynast. Even since abolition of the Austrian monarchy, Max 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, Viscount Linley, a nephew of Queen Elizabeth II through her sister, Princess Margaret, is in the line of succession to the British crown: in that sense he is a British dynast. Yet he is not a male-line member of the royal family, and is therefore not a dynast of the House of Windsor.
On the other hand, the German aristocrat Ernst August, Prince of Hanover (born 1954), a male-line descendant of George III of the United Kingdom, possesses no legal British name, titles or styles (although he is entitled to re-claim the once-royal dukedom of Cumberland), was born in the line of succession to the British crown and was bound by Britain's Royal Marriages Act 1772 until it was repealed when the Succession to the Crown Act 2013 took effect on 26 March 2015. Thus, in 1999 he requested and obtained formal permission from Elizabeth II to marry the Roman Catholic Princess Caroline of Monaco. Yet a clause of the English Act of Settlement 1701 remained in effect at that time, stipulating that dynasts who marry Roman Catholics are considered "dead" for the purpose of succession to the throne. That exclusion, too, ceased to apply on 26 March 2015, with retroactive effect for those who had been dynasts prior to triggering it by marriage to a Catholic.