Even to this day, the term ‘queer’ raises a number of questions for those who hear it. Who or what is ‘queer’? Is being lesbian or gay the same as being ‘queer’? Can ‘straight’ people ever be ‘queer’? The dictionary definition gives ‘eccentric’ as well as ‘homosexual’ and it is in this spirit of questioning what is ‘normal’, unsettling existing complacencies, and highlighting the dynamic and unpredictable nature of desire that Teresa de Lauretis coined the phrase ‘queer theory’ for the title of a conference at the University of California, Santa Cruz, in 1990. She also guest-edited the ‘Queer Theory’ issue of the journal Differences, which appeared a year later. Her work of the 1980s and 1990s laid many of the foundations of the field of queer studies, contributing to debates on lesbian spectatorship as well as offering a thoroughgoing critique of the heterosexist assumptions of most feminist theorizing on film. This chapter focuses on the exceptionally detailed theory of lesbian desire articulated in her book The Practice of Love, showing its power to illuminate lesbian films and cultural practices and situating this within the context of her other contributions to ‘queer theory’.