- John IV, King of Portugal, 1604-16561
- John Manuel, Prince of Portugal, 1537-15541
- John V, King of Portugal, 1689-17501
- John, Duke of Burgundy, 1371-14191
- John, the Apostle, Saint1
- Joseph (Son of Jacob)1
- Judaism--Customs and practices1
- Judaism--Doctrines1
- Judaism--Liturgy1
- Judeo-Arabic letters1
- Judges (Islamic law)1
- Judges--Selection and appointment1
- Julii family1
- Justice, Administration of1
- Jāmiʻ al-Azhar1
- Jāmiʻ al-ṣaḥīḥ (Bukhārī, Muḥammad ibn Ismāʻīl)1
- Kansas--Lawrence1
- Kemalpaşazade, 1468 or 1469-1534. Iṣlāḥ wa-al-īḍāḥ1
- Khabbāzī, ʻUmar ibn Muḥammad, 1231 or 1232-1292. Mughnī fī uṣūl al-fiqh1
- Khamti language1