Old Prussia may refer to different entities, which were also territorially defined.

In political and territorial respect it refers to:

• Old Prussia
• The Provinces of Prussia
  Provinces of Prussia
  The Provinces of Prussia constituted the main administrative divisions of Prussia. Following the dissolution of the Holy Roman Empire in 1806 and the Congress of Vienna in 1815 the various princely states in Germany gained their nominal sovereignty, but the reunification process that culminated in...
  
   officially formed in 1815 or partially later, whose territories belonged to the Kingdom of Prussia
  Kingdom of Prussia
  The Kingdom of Prussia was a German kingdom from 1701 to 1918. Until the defeat of Germany in World War I, it comprised almost two-thirds of the area of the German Empire...
  
   before 1815 or before 1866, especially:
  • in a narrow sense the expression means the entirety of the:
    • Province of Brandenburg
      Province of Brandenburg
      The Province of Brandenburg was a province of the Kingdom of Prussia and the Free State of Prussia from 1815 to 1946.-History:The first people who are known to have inhabited Brandenburg were the Suevi. They were succeeded by the Slavonians, whom Henry II conquered and converted to Christianity in...
      
      
    • Province of East Prussia
      Province of East Prussia
      The Province of East Prussia was a province of Prussia from 1773–1829 and 1878-1945. Composed of the historical region East Prussia, the province's capital was Königsberg ....
      
      
    • Province of Pomerania
    • Province of Prussia
      Province of Prussia
      The Province of Prussia was a province of the Kingdom of Prussia from 1829-1878 created out of the provinces of East Prussia and West Prussia....
      
      , combining East and West Prussia between 1829-1878
    • Province of Silesia
      Province of Silesia
      The Province of Silesia was a province of the Kingdom of Prussia from 1815 to 1919.-Geography:The territory comprised the bulk of the former Bohemian crown land of Silesia and the County of Kladsko, which King Frederick the Great had conquered from the Austrian Habsburg Monarchy in the 18th...
      
      
    • Province of West Prussia
  • in the broad sense of the expression the following provinces are also included:
    • Province of Hohenzollern
      Province of Hohenzollern
      Hohenzollern was a de facto province of the Kingdom of Prussia. It was created in 1850 by joining the principalities of Hohenzollern-Sigmaringen and Hohenzollern-Hechingen after both formerly independently ruling Catholic princely lines of the House of Hohenzollern had handed over their...
      
      
    • Rhine Province
      Rhine Province
      The Rhine Province , also known as Rhenish Prussia or synonymous to the Rhineland , was the westernmost province of the Kingdom of Prussia and the Free State of Prussia, within the German Reich, from 1822-1946. It was created from the provinces of the Lower Rhine and Jülich-Cleves-Berg...
      
      
    • Province of Westphalia
      Province of Westphalia
      The Province of Westphalia was a province of the Kingdom of Prussia and the Free State of Prussia from 1815 to 1946.-History:Napoleon Bonaparte founded the Kingdom of Westphalia, which was a client state of the First French Empire from 1807 to 1813...
      
      

In religious and territorial respect it refers to:

• Evangelical State Church of Prussia's older Provinces, renamed into Evangelical Church of the old-Prussian Union (1922-1953).

Source: Der Große Brockhaus: Handbuch des Wissens in zwanzig Bänden: 21 vols., 15th totally revised ed., Leipzig: F. A. Brockhaus, 1928-1935, vol. 1: A–Ast, article: 'Altpreußen', p. 356. No ISBN.