| Date | Publication | Publisher | Type | Page | |
|---|---|---|---|---|---|
| April 1967 |
|
Those Who Watch | Signet / New American Library | Novel | 5 |
| April 1967 |
|
Those Who Watch | Signet / New American Library of Canada | Novel | 5 |
| 1968 |
|
Os Vigilantes | Galeria Panorama | Novel | |
| June 1968 |
|
Ufos über der Erde | Moewig | Novel | |
| January 1971 |
|
Those Who Watch | Signet / New American Library of Canada | Novel | 5 |
| July 1973 |
|
Ufos über der Erde | Pabel-Moewig | Novel | 5 |
| September 1977 |
|
Those Who Watch | New English Library | Novel | 5 |
| April 1979 |
|
Those Who Watch | New English Library | Novel | 5 |
| May 1980 |
|
Gli osservatori | Editrice Nord | Novel | |
| November 1981 |
|
Beobachter aus dem All | Goldmann | Novel | |
| 1983 |
|
Those Who Watch | Signet / New American Library | Novel | 5 |
| 1983 |
|
Those Who Watch | Signet / New American Library of Canada | Novel | 5 |
| April 1987 |
|
Les guetteurs des étoiles | Presses Pocket | Novel | |
| October 1987 |
|
Those Who Watch | Signet / New American Library | Novel | 5 |
| February 1989 |
|
Gli osservatori | Editrice Nord | Novel | |
| September 2011 |
|
Those Who Watch | Gateway / Orion | Novel | |
| December 2022 |
|
Among Strangers | Subterranean Press | Omnibus | 13 |
| December 2022 |
|
Among Strangers | Subterranean Press | Omnibus | 13 |