In this paper, I first survey the ways in which bisexuality was understood by late 19^th-century sexologists, by Freud and his followers, by Alfred Kinsey, and by contemporary social scientists and political activists. Then the three domains distinguished by Freud in which bisexuality is currently being examined are surveyed: biological bisexuality, psychological bisexuality (in terms of gender), and kinds of object choice. Particular areas of research that indicate how questions about bisexuality are currently being considered are mapped, for example, transsexualism. The final part of the paper is an inquiry into the ways in which objects are bisexual, a domain that has been neglected in the complex history of work on bisexuality.