The Encyclopaedia of Sexual Knowledge, under the editorship of Dr. Norman Haire (1892–1952), is the first of a trilogy of sexual encyclopaedias by Arthur Koestler writing under the pen name of ‘Dr. A. Costler’. It is the English version, published by Koestler's cousin Francis Aldor in 1934, of the book L'encyclopédie de la vie sexuelle that Koestler in 1933 wrote, together with "A. Willy" (the pseudonym of his other cousin Willy Aldor) and the German Dr. Levy-Lenz. The second book is Sexual Anomalies and Perversions, Physical and Psychological Development, Diagnoses and Treatment. The title of the third book is, in the original French edition of 1939, L’Encyclopédie de la famille. This third book was subsequently translated into English and published under various titles and with changes t