Michel Foucault, The History of Sexuality Volume One: The Will To Knowledge, Penguin, London. (First published: 1976).

— Queer theory grew, basically, out of this book. Why? Because Foucault argues that the current Western social view of sexuality is not the sum total of knowledge gathered over the aons, but was invented last century. Our current discourses about homosexuality (or heterosexuality) suggest that these are distinct conditions, or identities; but to Foucault these are just labels put onto people because of some actions they may or may not engage in. In other societies which employ different discourses, these labels would just not make sense.

Foucault also argued that power is not possessed but is exercised; and the exercise of power produces a corresponding resistance. It is therefore partly because people try to shovel discourse about sexuality into the cupboard that it comes crashing out all over the place again.
[See the Foucault pages for more].