This book explores how the language of sexuality was codified in English dictionaries from 1604 to 1933, surveying the centuries before the coining of identity terms such as queer and heterosexual and then the decades when they had just begun entering wider currency. The introduction explains the temporal and spatial scope of the book and its understanding of sexuality and dictionary. It places the ideological histories of these two concepts in parallel, tracing how both became subject to the scientific spirit of the late nineteenth century—sexuality under the medical lens of sexology, lexicography under the empirical principles of the Oxford English Dictionary. Though prior studies that bring together lexicography and sexuality have been conducted within a range of disciplines, these have often occurred in isolation from each other. In an effort to bridge the divide between dictionary scholarship and queer linguistics in particular, the introduction puts forward an analytical framework which builds on the strengths of both research traditions. This is followed by an outline of how the discussion will be structured across the rest of the book.