Gella, Aleksander (1989). Development of Class Structure in Eastern Europe: Poland and Her Southern Neighbors. SUNY Press. стр. 217. ISBN9780887068331. Приступљено 20. 8. 2016. „'Oprichnina was originally a band of faithful servants organized by Ivan IV into a police force; they were used by the tsar to crush not only all boyars (Russian nobility) under suspicion, but also the Russian princes […]. Oprichnina enabled the tsars to build the first police state in modem history.”
Wilson, Colin (1964). Rasputin and the Fall of the Romanovs. стр. 60. Приступљено 20. 8. 2016. „[Ivan IV] established a political security force to run the Oprichina[sic], whose task was to spy on his enemies and destroy them; hence Ivan may be regarded as the inventor of the police state.”
Oxford English Dictionary, Third edition, January 2009; online version November 2010. [1]Архивирано на сајту Wayback Machine (28. септембар 2016); accessed 10. 4. 2019.
Oxford English Dictionary, Third edition, January 2009; online version November 2010. [1]Архивирано на сајту Wayback Machine (28. септембар 2016); accessed 10. 4. 2019.
