Honorary Membership was limited to 10 from 1890-1900, and to 15 from 1901 onwards. Corresponding Membership was a lesser class of Honoris causa membership in the early years. A few honorary members, such as Barnard, were first made corresponding members for a short time before being recommissioned as honorary members.
| Nation(s) | Start | End | |
|---|---|---|---|
| Bowen, Dr. Ira S. | USA | 1956 | 1973 |
| Brashear, Dr. John A. | USA | 1901 | 1920 |
| Brown, Dr. R. Hanbury | United Kingdom/Australia | 1987 | 2002 |
| Bruce, Mr. William | Canada | 1927 | 1927 |
| Burnham, Prof. Sherburne Wesley | USA | 1891 | 1921 |
| Campbell, Prof. William Wallace | USA | 1905 | 1938 |
| Christie, Dr. Sir Wm. Henry Mahoney | United Kingdom | 1891 | 1922 |
| Clemence, Dr. Gerald M. | USA | 1964 | 1974 |
| Clerke, Miss Agnes M. | United Kingdom | 1891 | 1907 |
| Crawford, Dr. David L. | USA | 1997 | 2024 |