APA (7th ed.) Citation

Küng, H., & Quinn, E. (1979). The Christian challenge: A shortened version of On being a Christian. Collins.

Chicago Style (17th ed.) Citation

Küng, Hans, and Edward Quinn. The Christian Challenge: A Shortened Version of On Being a Christian. London: Collins, 1979.

MLA (8th ed.) Citation

Küng, Hans, and Edward Quinn. The Christian Challenge: A Shortened Version of On Being a Christian. Collins, 1979.