His Eminence (abbreviation "H.Em.", oral address Your Eminence or Most Reverend Eminence) is a historical style of reference for high nobility, still in use in various religious contexts.
The style remains in use as the official style or standard of address in reference to a cardinal of the Roman Catholic Church, reflecting his status as a Prince of the Church.
A longer, and more formal, title is "His (or Your when addressing the cardinal directly) Most Reverend Eminence".
Patriarchs of Eastern Catholic Churches who are also cardinals may be addressed as "His Eminence" or by the style particular to Eastern Catholic patriarchs, His Beatitude.
When the Grand Master of the Military Order of the Knights of Malta, the head of state of their sovereign territorial state comprising the island of Malta until 1797, who had already been made a Reichsfürst (i.e., prince of the Holy Roman Empire) in 1607, became (in terms of honorary order of precedence, not in the actual church hierarchy of ordained ministers) the most senior official after the most junior member of the Cardinals in 1630, he was also awarded the hybrid style His Most Eminent Highness (abbreviation HMEH); to recognize his status as a type of prince of the Church. The Prince and Grand Master of the contemporary Sovereign Military Order of Malta is still syled His Most Eminent Highness. Styles such as "His Grand Eminence" or "His Eminent Grace" amongst others were used as well, some formalized by the Pope or other powers, such as monarchs. However, many others where simply personal preference of the Cardinal and by the merit of other earthly offices.
While the term is shunned by many individuals of other faiths or denominations of Christianity, the title is officially maintained in international diplomacy without regard for its doctrinal, philosophical and theological origins.