- Jiménez de Enciso, Diego1
- Jiménez de Enciso, Pedro1
- Joachim, Saint1
- John Chrysostom, Saint, -40718
- 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
- Juana, la Loca, Queen of Castile, 1479-15551
- Juana, of Austria, Princess of Portugal, 1535-15733
- Judaism2
- Judaism--Ari rite1
- Judaism--Customs and practices1
- Judaism--Prayers and devotions1
- Judeo-Arabic language1
- Judeo-Arabic literature2
- Judeo-Persian language1