By the Grace of God (Latin: '''Dei Gratia''', abbreviated D.G.) is a formulaic phrase used especially in Christian monarchies as an introductory part of the full styles of a monarch. For example in England and later the United Kingdom, the phrase was formally added to the royal style in 1521 and continues to be used. For example, on UK coinage, the abbreviation DG appears today.
See main article: Divine right of kings. Originally, it had a literal meaning: the divine right of kings was invoked—notably by Christian monarchs—as legitimation (the only one above every sublunary power) for the absolutist authority the monarch wielded, that is, the endorsement of God for the monarch's reign.
By custom, the phrase "by the Grace of God" is restricted to sovereign rulers; in the feudal logic, a vassal held fief not by the grace of God, but by grant of a superior noble. Yet this did not stop kings using it, even when they did homage to the pope (as vicegerent of God) or another ruler, such as the Kingdom of Bavaria, a state of the Holy Roman Empire.
Parallels exist in other civilizations, e.g. Mandate of Heaven of the Chinese empire, where for centuries the official decrees by the emperors of China invariably began with the phrase 「奉天承運皇帝，詔曰」 which is translated as "The Emperor, by the Grace of Heaven, decrees".
The traditional phrase "by the grace of God" is still included in the full titles and styles of the monarchs of Denmark, Liechtenstein, the Netherlands, Monaco and the United Kingdom.
In other Commonwealth realms, who share the same monarch with the United Kingdom, the style is used in Antigua and Barbuda, Australia, The Bahamas, Belize, Canada, Grenada, Jamaica, New Zealand, Solomon Islands, St. Kitts and Nevis, St Lucia, St. Vincent and the Grenadines, and Tuvalu. Papua New Guinea does not use the style.
The phrase was used in Luxembourg until 2000, when Henri, the current grand duke, decided to drop it. During the 20th century dictatorship of Francisco Franco in Spain, Spanish coins bore a legend identifying him as Francisco Franco Caudillo de España por la G de Dios ("Francisco Franco Caudillo of Spain by the G(race) of God").
The phrase is not used in the monarchies of Belgium, Luxembourg (Jean, abdicated 2000), Norway (Haakon VII, died 1957) and Sweden (Gustav VI Adolf, died 1973). In Spain, article 56(2) of the 1978 constitution, states that the title of the King of Spain is simply "King of Spain" (Rey de España) but that he "can use the titles that correspond to the Crown". As a result, the King of Spain may use "by the grace of God", but this is not used on official documents.
In some cases, the formula was combined with a reference to another legitimation, especially such democratic notions as the social contract, e.g.