- Author: Karsten Brüggemann, Ralph Tuchtenhagen
- Language: German
- Year: 2010
- Author: Joachim Tauber, Ralph Tuchtenhagen
- Language: German
- Year: 2008
- Author: Thomas Fliege, Silke Göttsch-Elten, Kaspar Maase, Ralph Winkle
- Language: German
- Year: 2010
- Author: Ralph Kunz, Isabelle Noth
- Language: German
- Year: 2012
- Author: Ralph Lindner, Karl-Siegbert Rehberg, Gisela Staupe
- Language: German
- Year: 2011
- Author: Ralph Hochschild
- Language: German
- Year: 1999
- Author: Ralph Jessen
- Language: German
- Year: 1991
- Author: Ralph Kauz, Morris Rossabi
- Language: German
- Year: 2022
- Author: Ralph Kunz
- Language: German
- Year: 2016
- Author: Rebecca Giselbrecht, Ralph Kunz
- Language: English
- Year: 2015