The early pioneers of the new field of sexology examined and classified sexual behaviours, identities and relations. For years much of the material has been "censored" in the sense that it has been difficult to obtain. This text brings together many of those documents of the modern science of sexuality. The extracts cover a variety of topics, including gender and sexual difference, homosexuality, trans-sexuality and bisexuality, heterosexuality, marriage and sex manuals, reproductive control, eugenics, race and various sexual proclivities.