D with stroke

A lowercase đ appeared alongside a lowercase retroflex D in a 1982 revision of the African reference alphabet. This revision of the alphabet eliminated uppercase forms, so there was no conflict between ɖ and đ.

Đ was used in Medieval Latin to mark abbreviations of words containing the letter d. For example, hđum could stand for heredum "of the heirs". Similar crossbars were added to other letters to form abbreviations.[4]

The crossed d was introduced by the Serbian philologist Đuro Daničić in 1878 for use in Serbo-Croatian in his Dictionary of the Croatian or Serbian Language, replacing the older digraphs dj and gj.[5] Daničić modeled the letter after the Icelandic and Anglo-Saxon letter eth, albeit representing a different sound, the affricate [dʑ].[5] In 1892 it was officially introduced in Croatian and Slavonian schools (in the Habsburg Kingdom of Croatia-Slavonia where the Croatian language was official) and so definitively added to Gaj’s Latin alphabet.[5] The letter thereafter gradually entered daily use,[5] spreading throughout Serbo-Croatian and then to Macedonian (its Latin transliterations are heavily influenced by Serbo-Croatian from the Yugoslav period).

The crossed d is today considered a distinct letter, and is placed between Dž and E in alphabetical order. Its Cyrillic equivalent is Ђ ђ.[5] Its partial equivalent in Macedonian is Ѓ ѓ (because only some dialects contain the /dʑ/ sound). When a true đ is not available or desired, it is transcribed as dj in modern Serbo-Croatian, and as gj in Macedonian. The use of dj in place of đ used to be more common in Serbo-Croatian texts, but it is falling out of practice.

An example of đ being used for a voiced dental fricative in the phonetic transcription of early Germanic languages, alongside ƀ for bilabial and ʒ for velar, from Joseph Wright's Old High German Primer (1906).

In the present-day orthographies of Northern Sámi, Inari Sámi and Skolt Sámi, đ represents the fricative [ð]. It is considered a distinct letter and placed between D and E in alphabetical order.

A page from the đ section of de Rhodes's Dictioniarum Annamiticum, a 1651 Vietnamese-Portuguese-Latin dictionary. As with the B with flourish, Đ only appears in lowercase in de Rhodes's works.

Đ is the seventh letter of the Vietnamese alphabet, after D and before E.[6] Traditionally, digraphs and trigraphs like CH and NGH were considered letters as well, making Đ the eighth letter.[7] Đ is a letter in its own right, rather than a ligature or letter-diacritic combination; therefore, đá would come after dù in any alphabetical listing.

Đ represents a voiced alveolar implosive (/ɗ/) or, according to Thompson (1959), a preglottalized voiced alveolar stop (/ʔd/).[8] Whereas D is pronounced as some sort of dental or alveolar stop in most Latin alphabets, an unadorned D in Vietnamese represents either /z/ (Hanoian) or /j/ (Saigonese).

The Vietnamese alphabet was formally described for the first time in the 17th-century text Manuductio ad Linguam Tunckinensem, attributed to a Portuguese Jesuit missionary, possibly Francisco de Pina[9] or Filipe Sibin.[10] This passage about the letter Đ was later incorporated into Alexandre de Rhodes' seminal Dictionarium Annamiticum Lusitanum et Latinum:[11]

Another letter written with the symbol đ is completely different than our own and is pronounced by raising the tip of the tongue to the palate of the mouth, immediately removing it, without in any way touching the teeth, for example đa đa: partridge. And this letter is very commonly used at the beginning of a word.

— Manuductio ad Linguam Tunckinensem[note 1]

On older typewriters, Đ was located where Z would be in the French AZERTY layout.[13] Alternatively, a hyphen can be overstruck onto a D.

On computers without support for a Vietnamese character set or Unicode, Đ is encoded as DD and đ as dd according to the Vietnamese Quoted-Readable standard. Vietnamese computer users typically input Đ as DD in the Telex and VIQR input methods or as D9 in the VNI input method. In the absence of an input method, the TCVN 6064:1995 and Microsoft Windows Vietnamese keyboard layouts map ZA0-09 (0 on a U.S. keyboard) to đ, or Đ when holding down ⇧ Shift. The Windows layout also maps ZA0-11 (=) to ₫.

Other modes of communication also have dedicated representations of Đ. In Vietnamese Braille, it is ⠙, which corresponds to D in French Braille. In the Vietnamese manual alphabet, Đ is produced by touching the thumb to the index finger. In Morse code, it is rendered – · · – · ·, corresponding to Telex's "DD".[14]

The Spanish language uses Đ as a ligature of the word "de" (Spanish for "of"). It is rarely typed, but commonly used on signs and in handwritten text.

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  Sign with the letter Đ, in Oaxaca, Mexico
• 
  Spanish letter Đ, in the font Coruña

The lowercase đ is used in some phonetic transcription schemes to represent a voiced dental fricative [ð] (English th in this). Eth (ð) is more commonly used for this purpose, but the crossed d has the advantage of being able to be typed on a standard typewriter, by overlaying a hyphen over a d.[15]

A minuscule form of the letter, đ, is the symbol of the đồng, the currency of Vietnam, by a 1953 decree by Hồ Chí Minh.[16] The South Vietnamese đồng, on the other hand, was symbolized "Đ.", in majuscule. In Unicode, the Vietnamese đồng symbol is properly represented by U+20AB ₫ DONG SIGN, but U+0111 đ LATIN SMALL LETTER D WITH STROKE is often used instead. In Vietnamese, the đồng sign is written after the amount in superscript, often underlined.

The uppercase form, Ð, is used as the currency symbol for the cryptocurrency Dogecoin.

Dispersity is represented by the symbol Đ, and is a measure of the heterogeneity of sizes of molecules or particles in a mixture, referring to either molecular mass or degree of polymerization.

In Japanese handwriting, the letter D may be written as Đ to clearly distinguish it from the letter O or the digit 0. This is similar to writing Z or 7 with a bar to distinguish them from 2 and 1 respectively.