The Diogenes Club is a club featured in a few Sherlock Holmes stories written by Sir Arthur Conan Doyle, most notably "The Greek Interpreter". Probably named after Diogenes the Cynic, it was co-founded by Sherlock's older brother, Mycroft Holmes. It is a place where men can go to read without any distractions. The number one rule is that there is no talking.

"...There are many men in London, you know, who, some from shyness, some from misanthropy, have no wish for the company of their fellows. Yet they are not averse to comfortable chairs and the latest periodicals. It is for the convenience of these that the Diogenes Club was started, and it now contains the most unsociable and unclubable men in town. No member is permitted to take the least notice of any other one. Save in the Stranger's Room, no talking is, under any circumstances, allowed, and three offences, if brought to the notice of the committee, render the talker liable to expulsion. My brother was one of the founders, and I have myself found it a very soothing atmosphere."

--Sherlock Holmes's description of The Diogenes Club in "The Adventure of the Greek Interpreter"

Although there is no hint in the Canon that the Diogenes Club is anything but what it seems to be, several later writers have made use of the idea that the club was founded as a front for the British secret service. The idea appears to have originated in the Billy Wilder film The Private Life of Sherlock Holmes. It has been extensively exploited by British fantasy writer Kim Newman, who has written a series of stories chronicling the activities of his version of the Club ("an institution that quietly existed to cope with matters beyond the purview of regular police and intelligence services") through the 20th century and into the 21st.