Although originally a title reserved for royalty, select nobles, and church hierarchs, it is now often used as a mark of esteem for a person of personal, social or official distinction, such as a community leader of long standing, a person of significant wealth, or a noble, but may also be used ironically. As a style, rather than a title or rank, it is used with, and not instead of, a person's name.
Syntactically, it is used in much the same way (although for a broader group of persons) as "Sir" and "Dame" are used in English when speaking of or to a person who has been knighted, e.g. "Don Firstname" or "Doña Firstname Lastname". Unlike "The Honourable" in English, Don may be used when speaking directly to a person, and unlike "Mister" it must be used with a given name. For example, "Don Diego de la Vega," or (abbreviating "señor") "Sr. Don Diego de la Vega," or simply "Don Diego" (the secret identity of Zorro) are typical forms. But a form like "Don de la Vega" is not correct and would never be used by Spanish speakers. "Señor de la Vega" should be used instead.
In North America, Don has also been made popular by films depicting the Mafia, such as The Godfather series, where the crime boss would claim for himself the signs of respect that were traditionally granted in Italy to nobility. This usage of the honorific in these films (e.g. Don Corleone, Don Barzini, etc.) is not common or correct in normal historic usage in Italy. The proper Italian usage is similar to the Castilian Spanish usage mentioned in the previous paragraph.
Historically, don was used to address members of the nobility, e.g. hidalgos and fidalgos, as well as members of the secular clergy. The treatment gradually came to be reserved for persons of the blood royal, and those of such acknowledged high or ancient aristocratic birth as to be noble de Juro e Herdade, that is, "by right and heredity" rather than by the king's grace. However, there were rare exemptions to the rule, such as the mulatto Miguel Enríquez, who received the distinction from Philip V due to his privateering work in the Caribbean. But by the twentieth century it was no longer restricted in use even to the upper classes, since persons of means or education (at least of a "bachiller" level), regardless of background, came to be so addressed and, it is now often used as if it were a more formal version of Señor, a term which was also once used to address someone with the quality of nobility (not necessarily holding a nobiliary title). This was, for example, the case of military leaders addressing Spanish troops as "señores soldados" (gentlemen-soldiers). In Spanish-speaking Latin America, this honorific is usually used with people of older age.
During the reign of King Juan Carlos of Spain from 1975 until his abdication as monarch on 19 June 2014, he was titled Su Majestad [S.M.] el Rey Juan Carlos (His Majesty King Juan Carlos). Following the abdication, Juan Carlos and his wife are titled, according to the Royal Household website, S.M. el Rey Don Juan Carlos (H.M. King Juan Carlos) and S.M. la Reina Doña Sofía (H.M. Queen Sofía)—the same as during his reign, with the honorific Don/Doña prefixed to the names. Juan Carlos' successor is S.M. el Rey Felipe VI.
In Spanish Colonial Philippines, the honorific title was reserved to the nobility, the Datu known as the Principalía, whose right to rule was recognised by Philip II on 11 June 1594.
The honorific was also used among Ladino-speaking Sephardi Jews, as part of the Spanish culture which they took with them after the Expulsion of the Jews from Spain in 1492.
The honorific title Don is widely used in the Americas. This is the case of the Mexican New Age author Don Miguel Ángel Ruiz, the Chilean television personality Don Francisco, and the Puerto Rican industrialist and politician Don Luis Ferré, among many other figures. The title Don is considered highly honorific, more so than, for example, academic titles such as "Doctor" or than political titles such as "Governor." For example, although Puerto Rican politician Pedro Albizu Campos had a doctoral degree, he has been titled Don. Likewise, Puerto Rican Governor Luis Muñoz Marín has often been called Don Luís Muñoz Marin instead of Governor Muñoz Marin. In the same manner, Don Miguel Ángel Ruiz is an M.D.
Prior to the American conquest of the Southwest, a number of Americans immigrated to California, where they often became Mexican citizens and changed their given names to Spanish equivalents, for example "Juan Temple" for Jonathan Temple. It was common for them to assume the honorific "don" once they had attained a significant degree of distinction in the community.
Today in the Americas, and in Mexican-American communities, the title Don or Doña is used in honorific form when addressing a senior citizen.
The usage of Dom was a prerogative of princes of the royal blood and also of other individuals to whom it had been granted by the sovereign. In most cases, the title was passed on through the male line. Strictly speaking, only females born of a nobleman bearing the title Dom would be addressed as Dona, but the style was not heritable through daughters. The few exceptions depended solely on the conditions upon which the title itself had been granted. A well-known exception is the descent of Dom Vasco da Gama.
There were many cases, both in Portugal and Brazil, in which the title of Dom (or Dona) was conceded to, and even bought by, people who were not from the royalty. In any case, when the title was officially recognized by the proper authority, it became part of the name.
Today, in Portugal and Brazil, Dom is ordinarily employed only for higher members of the clergy, and for superiors of religious orders, such as the Order of Saint Benedict, wherein it is also associated with the status of Dom Frater. Dom is similarly used within the Benedictine Order throughout France and the English speaking world. In France, it is also used within the male branch of the Carthusian Order.
In the Portuguese language, the female, Dona (or, more politely, Senhora Dona), has become common when referring to a woman who does not hold an academic title. It's commonly used to refer to First Ladies, although less common for female politicians.
Officially, Don was the style for a principe or duca (and any legitimate, male-line descendant thereof) who was a member of the nobility (as distinct from a reigning prince or duke, who was generally entitled to some form of the higher style of Altezza). This was how the style was used in the Almanach de Gotha for extant families in its third section. The feminine, "Donna", was borne by their wives and daughters. The last official Italian nobility law (not legally effective since 1948) stated that the style belonged to all members of the following families:whose main title is principe or duca (both as the eldest male title or all members title);
who have had a special grant;
who belong to ancient Lombardy (duchy of Milan) and to whom it had been recognized;
Sardinian families who bear both the titles of hereditary knight and nobleman/noblewoman (whatever the main title of the family).
Genealogical databases and dynastic works still reserve the title for this class of noble by tradition, although it is no longer a right under Italian law.
In practice, however, the style Don/Donna (or Latin Dominus/Domina) was used more loosely in church, civil and notarial records. The honorific was often accorded to the untitled gentry (e.g., knights or younger sons of noblemen), priests, or other people of distinction. It was, over time, adopted by organized criminal societies in Southern Italy (including Naples, Sicily, and Calabria) to refer to members who held considerable sway within their hierarchies.
Today in Italy, the title is usually only given to Roman Catholic diocesan priests (never for prelates, who bear higher honorifics such as monsignore, eminenza, and so on). In Sardinia, until recently it was commonly used for nobility (whether titled or not), but it is being presently used mainly when the speaker wants to show that he or she knows the don's condition of nobility.
Outside of the priesthood or old nobility, usage is still common in the south, mostly as an honorific form to address the elderly, but rarely if ever used in central or northern Italy. It can be used satirically or ironically to lampoon a person's sense of self-importance.
As in the Spanish usage, Don is prefixed either to the full name or to the person's given name, including crime bosses.
The form "Don Lastname" for criminals (as in Don Corleone) is an American custom. In southern Italy, mafia bosses are addressed as "Don Firstname" by other criminals and sometimes their victims as well, while the press usually refers to them as "Firstname Lastname", without the honorific.
Priests are the only ones to be referred as Don Lastname by the Italian press, although when talking directly to them they are usually addressed as Don Firstname, which is also the most widely form used by parishioners when referring to their priest.
At Oxford University, a member of the academic staff is sometimes referred to as a don. In practice it is most commonly used to refer to fellows of the colleges.
The Don is the official mascot of the athletic teams fielded by the University of San Francisco.