| Jurisdiction: | Diocese |
| Latin: | Dioecesis Aquisgranensis |
| Local: | Bistum Aachen |
| Coat: | Coat of arms of Diocese of Aachen.png |
| Coat Size: | 120x100px |
| Aachen | |
| Country: |  Germany |
| Metropolitan: | Archdiocese of Cologne |
| Denomination: | Roman Catholic |
| Rite: | Roman Rite |
| Established: | 1802 (re-established 13 August 1930) |
| Area Km2: | 3,937 |
| Population: | 2,028,699 |
| Population As Of: | 2012 |
| Catholics: | 1,110,948 |
| Catholics Percent: | 54.8 |
| Bishop: | Helmut Dieser |
| Auxiliary Bishops: | Karl Borsch |
| Vicar General: | Andreas Frick |
| Cathedral: | Aachen Cathedral |
| Parishes: | 538 |
| Priests: | 535 |
| Patron: | Mary, Mother of Jesus |
| Map: | Karte Bistum Aachen.png |
The Diocese of Aachen (Latin: Dioecesis Aquisgranensis) is a Latin diocese of the Catholic Church located in Germany and one of the six dioceses in the ecclesiastical province of Cologne. The incumbent bishop is Helmut Dieser, who was appointed by Pope Francis on 23 September 2016. The bishop's seat is Aachen.
The diocese is located in the very west of Germany, extending from Krefeld in the north to the mountainous Eifel area in the south. Bordering dioceses are Cologne, Münster, Essen and Trier in Germany, Liège in Belgium and Roermond in the Netherlands.
The diocese is divided into seven regions which are in turn further subdivided into 538 parishesː
The bishop emeritus of Aachen is Heinrich Mussinghoff. There are two auxiliary bishops, Johannes Bündgens and Karl Borsch. Also, there are two emeritus auxiliary bishops, Gerd Dicke and Karl Reger. The vicar general is Andreas Frick.
| Tenure | Incumbente | Notes | |
|---|---|---|---|
| 9 May 1802 – 13 August 1809 | Marc Antoine Berdolet | Installed 25 July 1802; died in office | |
| 1825 | Diocese abolished | ||
| 1930 | Diocese re-established | ||
| 30 January 1931 – 5 October 1937 | Joseph Vogt | Ordained 19 March 1931; installed 25 March 1931; died in office | |
| 7 September 1943 – 19 May 1954 | Johannes Joseph van der Velden | Priest of Köln Cologne; ordained 10 October 1943; died in office | |
| 30 August 1954 – 13 December 1974 | Johannes Pohlschneider | Priest of Münster; ordained 18 November 1954; retired | |
| 9 September 1975 – 23 January 1994 | Klaus Hemmerle | Priest of Freiburg im Breisgau; ordained 8 November 1975; died in office | |
| 12 December 1994 – 8 December 2015 | Heinrich Mussinghoff | Priest of Münster; Ordained 11 February 1995 |
| Tenure | Incumbent | Notes | |
|---|---|---|---|
| 1931–1943 | Hermann Joseph Sträter | Ordained 16 October 1931, became Apostolic Administrator 15 May 1938, died 16 March 1943 | |
| 1938–1969 | Friedrich Hünermann | Ordained 3 December 1938, died 15 February 1969 | |
| 1961–1979 | Joseph Ludwig Buchkremer | Ordained 21 December 1961, retired 4 October 1979 | |
| 1970–2003 | Ernst Franz Gerd Werner Dicke | Ordained 11 April 1970, retired 21 November 2003 | |
| 1978–1980 | Maximilian Goffart | Ordained 18 February 1978, died 17 July 1980 | |
| 1981–1986 | Augustus Peters | Ordained 6 April 1981, died 3 May 1986 | |
| 1987–2006 | Karl Reger | Ordained 7 February 1987, retired 15 March 2006 | |
| 2003–present | Karl Borsch | Ordained 17 January 2004 | |
| 2006–present | Johannes Bündgens | Ordained 20 May 2006, retired 8 November 2022 |
Historically, today's territory of the Diocese of Aachen belonged to the Diocese of Liège and the Archdiocese of Cologne. The diocese was first created in 1802, covering the area west of the Rhine formerly belonging to Cologne, as well as parts from the dioceses Liège, Utrecht, Roermond and Mainz. After the first bishop Marc Antoine Berdolet died in 1809, Pope Pius VII refused to commission the successor suggested by Napoleon, Jean Denis François Camus. After the French rulership over the area, the diocese was abolished by the bull De salute animarum of July 16, 1821, and incorporated into the archdiocese of Cologne.
On August 13, 1930 the diocese was re-established by the papal bull Pastorale officii nostri. Joseph Vogt was appointed as its first bishop.
The principal church of the diocese is the Aachen Cathedral, of which the central part, the Palatine Chapel, was built in 800 under Charlemagne. It was also the first German World Heritage Site, inscribed in 1978.
The diocese has two churches that have been given the status of basilica minorː