Adnan (Arabic: عدنان, romanized: ʿAdnān) is traditionally regarded as the patriarch of the Adnanite Arabs, a major Arab lineage that historically inhabited Northern, Western, Eastern, and Central Arabia. The Adnanites are distinct from the Qahtanite Arabs of Southern Arabia, who trace their lineage to Qahtan.

Adnan is considered a direct descendant of the prophet Abraham (Ibrahim) through his son Ishmael (Ismāʿīl). His genealogy is of great significance in Arab and Islamic tradition, as the Islamic prophet Muhammad is said to descend from him. Adnan’s lineage connects him to a broad network of Arab tribes that played a crucial role in pre-Islamic and Islamic history.

According to historical Arab genealogies, Adnan was a key figure in the continuation of Ishmaelite ancestry among the Arabs. His descendants, known as the Adnanites, included prominent tribes such as Mudar, Rabi'ah, Quda'a and Qays ʿAylān, many of whom became dominant in the Arabian Peninsula. The Quraysh tribe, from which Muhammad emerged, is one of the most well-known Adnanite groups.

Due to the oral transmission of genealogies in early Arabia, the exact number of generations between Adnan and Ishmael remains uncertain, with various historical sources offering differing accounts. However, Adnan’s name is widely recognized in Islamic literature, Arab poetry, and pre-Islamic genealogical records.

According to tradition, Adnan is the father of a group of the Ishmaelite Arabs who inhabited west and northern Arabia; he is believed to be a descendant of Ishmael, son of Abraham. Adnan is believed by genealogists to be the father of many Ishmaelite tribes along the Western coast of Arabia, northern Arabia and Iraq.

Many family trees have been presented for Adnan, which do not agree about the number of ancestors between Ishmael and Adnan but agreed about the names and number of the ancestors between Adnan and the Islamic prophet Muhammad. Muhammad claimed that he descended from Ibrahim (Abraham) through Ishmael, in an unprecedented move, so in post-Islamic traditions Adnan is a descendant of Abraham, this modification was also carried over to the Banu Hashim branch of the Quraysh, but as Islam spread some other tribes also laid claim on the extension of the tree to Abraham, such as the Hawazin.

The overwhelming majority of traditions and Muslim scholars state that Adnan is a descendant of Qedar the son of Ishmael, except for Ibn Ishaq who claimed that Adnan was a descendant of Nebaioth. According to classical Muslim historian Al-Tabari, Ibn Ishaq's differing record may be due to one of the descendants of Qedar also bearing the name of "Nebaioth".

Most Muslim scholars refused any attempt to recite the ancestors between Adnan to Ishmael, and condemned other scholars such as Ibn Ishaq for doing it. This partial absence of evidence for any ancestor between Adnan and Ishmael (and his son) has led some scholars to consider any personal name between the two figures as post-Islam apocrypha.