- John I, King of Portugal, 1357-14331
- John II, King of Aragon, 1397-14791
- John IV, King of Portugal, 1604-16561
- John Manuel, Prince of Portugal, 1537-15541
- John V, King of Portugal, 1689-17501
- John VIII Palaeologus, Emperor of the East, 1392-14481
- Joseph (Son of Jacob)1
- Judaism1
- Judaism--Ari rite1
- Judaism--Prayers and devotions1
- Judeo-Arabic language1
- Judeo-Persian language1
- Julius III, Pope, 1487-15551
- Jurisprudence1
- Jurjānī, ʻAlī ibn Muḥammad, al-Sayyid al-Sharīf, 1340-1413. Ḥāshiyah ʻalá Taḥrīr al-qawāʻid al-manṭiqīyah1
- Jābir ibn Ḥayyān1
- Jāmiʻ al-Azhar1
- Jāmiʻ al-Muẓaffarī (Damascus, Syria)1
- Jāmiʻ al-ṣaḥīḥ (Bukhārī, Muḥammad ibn Ismāʻīl)1
- Kanz al-daqāʼiq (Nasafī, ʻAbd Allāh ibn Aḥmad)1