INTRODUCTIONKarl Heinrich Ulrichs (1825-1895) was a pivotal if enigmatic figure in the emerging historical discourse of modern sexuality. With no precedent or template to follow, he single-handedly launched a campaign of literary activism advocating for the rights of men who were sexually attracted to other men, publishing 12 books between 1864 and 1880. 1 He called these men 'urnings' and the men attracted to the opposite sex, 'dionings.' 2 A lawyer by training, he based his arguments on contemporary medical knowledge and was influential on the emerging sexual sciences.Scholarship has only turned his way within the last 50 years. More than a century elapsed between his main years of activity and the first historical appraisal. Much of what we know of Ulrichs came from his surviving correspondence. In contrast to his published works, the correspondence offers tantalising insights into Ulrichs' intellectual world and networks of exchange. They also reveal facets of his character that extend our under-standing of the man himself. Tragically, for the historian of sexuality, many of Ulrichs' personal papers and letters were confiscated and then lost by the state and the remainder destroyed in a house fire in 1893. It is likely that many of the letters he wrote to others were also destroyed. Despite this, from the letters that have survived, historians can glean biographical details, insights into motivations and emotional responses and map out how other individuals reacted to Ulrichs and his campaign of literary activ-