In the fictional universe of Spider Robinson, Callahan's Place is a bar with strongly community-minded and empathic clientele. It appears in the "Callahan's Crosstime Saloon" stories (compiled in the first novel of the same name, along with in its sequels "Time Travellers Strictly Cash" and "Callahan's Place"; most of the beloved barflies appear in the further sequels "The Callahan Touch"; "Callahan's Legacy"; "Callahan's Key"; and "Callahan's Con") and computer game.

The bar is run by Mike Callahan. The regulars are welcoming and willing to listen to any visitor's problems, no matter how strange, but do not snoop if a visitor is unwilling to share. Strange and unusual events and visitors turn up with frequency in the stories. Regulars at Callahan's include a talking dog, several extraterrestrials and time-travelers, a vampire, a couple of Irish mythological beings, and an obscenity-spewing parrot. The stories make heavy use of puns.

Lady Sally McGee, the madam of a house of excellent repute (and Mike Callahan's wife), stars in Robinson's "Callahan's Lady" and "Lady Slings The Booze." The regulars at Lady Sally's brothel (where the employees are "artists" and the patrons are "clients") insist on the same empathy and humor as those at Callahan's, and they are just as likely to have fantastic backgrounds.

Lady Sally's last name is almost certainly a tribute to the fictional character Travis McGee who appeared in a number of novels by John D. MacDonald.

This is the source of Callahan's Law - "Shared pain is lessened; shared joy, increased —thus do we refute entropy."

The series has a related Usenet newsgroup, alt.callahans, and IRC channel, #callahans, for fans.