Game Without Rules is a short story collection by the British crime and spy writer Michael Gilbert featuring his counter-intelligence agents Calder and Behrens.

The book contains the following stories, most of which were originally published in Ellery Queen's Mystery Magazine between 1962 and 1967:[3] The collection features two of Gilbert's most popular characters, the amiable elderly spies Daniel John Calder and Samuel Behrens.

[5] The mystery critic Anthony Boucher called Game without Rules the second-best volume of spy short stories ever published, next only to Somerset Maugham's Ashenden.

[7] The New York Times Book Review called the stories "entertaining and exciting", and found it hard to say which element was the most effective: the smooth ingenuity of plotting, the disconcerting combination of elegance and harshness, or the shock of amoral realism.

[9] In a 1984 essay, George N Dove considered that one of the reasons for the lasting popularity of Calder and Behrens was the happy contrast between their outward appearance of elderly, quiet gentility and the pair's ability to take forceful action.