Though conceived earlier, and though quite an independent work, Fundamentals in Sexual Ethics forms a natural sequel to my previous book, The Introduction to the Physiology and Psychology of Sex. The ideas formulated in the Ethics are built, as it were, upon a substructure of biological and physio-psychological facts, the interpretation of which is unavoidably coloured by the ubiquitous element of the 'personal equation.' This statement is necessary in order to enable the reader, and especially the ever ready critic, to form a just estimate of the opinions here offered.<br><br>I am under a deep obligation to Mr. Havelock Ellis. Not only have his works on Sex Psychology been a source of inspiration to me, but his generous assistance by the gift of some of his latest essays and the loan of books, including a Ms. work of the late Mrs. Havelock Ellis, has been invaluable.<br><br>I also owe a great debt of gratitude to my wife, without whose unwearying and discriminating advice this book would not be what it is.<br><br>Mr. David Isaacs has given his kind assistance in seeing this book through the press, for which my thanks are due to him.