1920s Investigators' Companion is a role-playing game supplement for Call of Cthulhu by Keith Herber, published by Chaosium.

Because modern game players may not know much about the early part of the twentieth century, 1920s Investigators' Companion contains information covering the 1920s.

[1] The book covers economic and social background, popular culture, research facilities, transportation, and equipment that would be available to 1920 investigators.

[2] In the October 1994 edition of Dragon (Issue 210), Rick Swan was impressed by the large volume of facts and figures, but questioned the book's usefulness, saying "Is the Companion interesting?

Swan concluded by giving the book an average rating of 3 out of 6, commenting, "This is mostly window dressing, helpful for spicing up a referee's descriptions, but unnecessary for players.