Kirc - Late
- Kircher, Athanasius
- Kirkwall
- Kisfaludy
- Kiss
- Klaczko, Julian
- Klee, Heinrich
- Klemens Maria Brentano
- Klesl, Melchior
- Kleutgen, Josef Wilhelm Karl
- Klinkowström
- Klopp, Onno
- Knabl, Joseph
- Kneeling
- Kneeling and Genuflection
- Kneipp, Sebastian
- Knight, Venerable William
- Knighthood
- Knighton, Henry
- Knights of Christ, Order of the
- Knights of Columbus
- Knights of Malta
- Knights of the Cross
- Knights of the Holy Sepulchre
- Knights of the Redeemer
- Knights Templars, The
- Knoblecher, Ignatius
- Knoll, Albert (Joseph)
- Knowledge
- Knowledge of Jesus Christ
- Knownothingism
- Knox, John
- Kober, Franz Quirin von
- Koberger, Anthony
- Kobler, Andreas
- Kochanowski, Jan
- Kochowski, Vespasian
- Kögler, Ignaz
- Kohlmann, Anthony
- Koller, Marian Wolfgang
- Konarski, Stanislaus