- Author: Helmut Merkel
- Language: German
- Year: 1991
- Author: Helmut Merkel
- Language: German
- Year: 2020
- Author: Helmut Merkel Peter Breuer Christoph Eltze Jürgen Kerner (auth.)
- Language: German
- Year: 2008
- Author: Helmut Merkel Franco Ronchi (editor)
- Language: Italian
- Year: 1997
- Author: Helmut Merkel Peter Breuer Christoph Eltze Jürgen Kerner (auth.)
- Language: German
- Year: 2008
- Author: Helmut Merkel
- Language: German
- Year: 1998