Gender is a very old conceptual category, but a relatively new framework for historical analysis. Sexuality is also a relatively new category of historical study, inspired in part by the gay liberation movement that began in the 1970s. This chapter focuses on three topics that each involved both gender and sexuality: migration, intermarriage and the cross-cultural blending that resulted from these; third- and transgenders; and religious transformations. The contacts between cultures before 1400 that changed gender structures had often been carried out through the transmission of ideas and construction of institutions by individuals or small groups of people. Laws regarding intermarriage were usually framed in gender-neutral language by lawmakers. Migration not only brought men and women from different groups together, but also introduced explorers, soldiers, settlers and officials to individuals who were understood in their own societies to be a third or fourth gender.