Ja'far ibn Mansur al-Yaman (Arabic: جعفر بن منصور اليمن) was an Isma'ili missionary (dāʿī) and theological writer of the 10th century. Originally born and raised in Yemen, where his father Ibn Hawshab had established the Isma'ili daʿwa in the late 9th century, he fled the country to the court of the Fatimid caliphs in Ifriqiya, where he remained until his death. He composed poems in praise of the Fatimids' victory over the uprising of Abu Yazid, a biography of his father, and authored or compiled a number of important theological treatises.