- Jihad1
- Jiménez de Cisneros, Francisco, 1436?-15171
- Jinn1
- Job (Biblical figure)1
- 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
- John the Baptist's Day1
- Joseph Della Reina, active 15th century1
- Judaism (Christian theology)1
- Judaism--Apologetic works1
- Judaism--Sephardic rite--Liturgy1
- Judas Iscariot1
- Judicial power (Islamic law)1
- Judicial process (Islamic law)1
- Julian, of Eclanum, Bishop, 380-approximately 4551
- Julius III, Pope, 1487-15551
- Jurjānī, ʻAlī ibn Muḥammad, al-Sayyid al-Sharīf, 1340-1413. Risālah al-kubrá fī al-manṭiq1