Book excerpt: Introduction : women and sexology : knowledge, possibilities, and problematic legacies -- The emergence of sexology in early twentieth century Germany -- As natural as eating, drinking, and sleeping : redefining the female sex -- Challenging the limits of sex : envisioning new gendered subjectivities and sexualities -- Troubling normal, taking on patriarchy : criticizing male (hetero)sexuality -- The erotics of racial regeneration : eugenics, maternity, and sexual -- New social and moral values will have to prevail : negotiating crisis and opportunity in the First World War -- Fluid gender, rigid sexuality : constrained potential in the post-war period