- Author: Dr Ross Campbell
- Language: English
- Author: Gary Chapman, Ross Campbell
- Language: English
- Year: 2016
- Author: Ross Campbell
- Language: Spanish
- Year: 1992
- Author: Ross Campbell
- Language: English
- Year: 2007
- Author: Gary Chapman Ross Campbell
- Language: English
- Year: 2011
- Author: Gary Chapman Ross Campbell
- Language: English
- Year: 2016
- Author: Ross Campbell
- Language: English
- Year: 2006
- Author: Ross Campbell
- Language: English
- Year: 2015
- Author: D. Ross Campbell
- Language: English
- Year: 1977
- Author: Gary Chapman, Ross Campbell
- Language: Portuguese
- Year: 2020