Author
- Johannes Mellarinus1
- Johannes Schöner1
- Johannes Tostius1
- Johannes de Sacrobosco1
- Johannes von Kastl1
- John Chrysostom1
- John Cornelius1
- John Frederick II of Saxony1
- John XXI1
- John of Ibelin1
- John Dokeianos1
- Joseph ben Ephraim Karo1
- Joseph ben Moses Sarfati1
- Joshua Benzion Segre1
- Juan de Torquemada1
- Kamal al-Din ibn al-Humam1
- Kamāl al-Dīn Turkumānī1
- Khaqani1
- Kingdom of Bohemia1
- Konrad III. von Soltau1