  While homosexuality was removed from the DSM as a diagnostic category in 1973, transsexuality was added in the 1980 DSM-III. However, the view of transsexuality and other trans-related phenomena as psychiatric and/or medical conditions has a much longer history. To be sure, not all accounts of trans phenomena were pathologizing (indeed, some aimed at political liberation). However, it is clear that early scholarly discussion of trans phenomena unfolded within the field of sexology—the “scientific” study of human sexuality. Some of the most notable thinkers include Karl Heinrich Ulrichs, Richard von Krafft-Ebing ([1886] 1965), Havelock Ellis ([1905] 1942), and Magnus Hirshfeld ([1910] 1991).