For the Croatian and Vietnamese letter that looks similar to Ð see D with stroke

Ð (capital Ð, lower-case ð) (or eth, eð or edh, Faroese: edd) is a letter used in Old English (Anglo-Saxon) and present-day Icelandic and Faroese. The letter had its origin as a d with a cross-stroke added. The lowercase version has retained the curved shape of a medieval scribe's d, which d itself has not.

In Icelandic, ð represents a voiced dental fricative, as in th in English "them". (As a point of curiosity, however, the name of the letter is pronounced eþ, i. e. voiceless, unless followed by a vowel.) In Faroese, ð is never pronounced, except ð before r as [g] in a few words. In the Icelandic and Faroese alphabets, ð follows d. In Anglo-Saxon, ð may represent the same sound as in Icelandic, or the voiceless th of "thread", both of which were also represented by thorn (þ). Eth was usually used when the diagraph was voiced (as in "the" or "that"). In Middle English, ð was no longer used; the Normans did not like characters in English which did not exist in the Latin alphabet. Ð was replaced with th, unfortunately making the voiced consonant indistinguishable from the unvoiced one, as the letter þ was also replaced by this digraph.

Lower-case eth is used as a symbol in the International Phonetic Alphabet, again for a voiced dental fricative, and in IPA usage, the name of the symbol is pronounced with the same voiced sound, as .