In current sociological work, bisexuality predominantly refers either to the sexual orientation of people who are attracted to people of more than one sex or gender, or to the sexual identity of people who have same-sex and different-sex sexual and/or romantic attraction. This entry discusses the different meanings of bisexuality throughout history but mainly focuses on the current meanings, main themes of bisexuality research, achievements, and challenges that bisexuality research is facing in order to become part of mainstream sociology and sexuality scholarship.