This thesis challenges the traditional view of the "femme fatale" as merely a dangerous and ravenous sexual predator who leads men into ruination. Critical, especially feminist, scholarship mostly regards the femme fatale as a sexist construction of a male fantasy and treats her as an expression of misogyny that ultimately serves to reaffirm male authority. But this thesis proposes alternative ways of viewing the femme fatale by showing how she can also serve as a figure for imagining female agency. As such, I focus on a particular character type that is distinct from the general archetype of the femme fatale because of the greater degree of agency she demonstrates. This "criminal femme fatale" uses her sexual appeal and irresistible wiles both to manipulate men and to commit criminal acts, usually murder, in order to advance her goals with deliberate intent and full culpability. This thesis reveals and explains the agency of the criminal femme fatales in American Hardboiled crime fiction between the late 1920s and the end of World War II in the works of three authors: Dashiell Hammett, Raymond Chandler and James M. Cain. The criminal femme fatales in the narratives of these authors show a subversive power and an ability to act - even though, or perhaps only if, this action is a criminal one. I show that these criminal femme fatales exhibit agency through their efforts to challenge not only the "masculine" genre and the criminal space that this genre represents, but also to undercut the male protagonist's role and prove his failure in asserting control and dominance. Hammett's narratives provide good examples of how the criminal femme fatales function on a par with male gangsters in an underworld of crime and corruption. Chandler's work demonstrates a different case of absent/present criminal women who are set against the detective and ultimately question his power and mastery. Cain's narratives show the agency of the criminal femme fatales in the convergence between their ambition for social mobility and their sexual power over the male characters. To explain how these female characters exhibit agency, I situate this body of literature alongside contemporaneous legal and medical discourses on female criminality. I argue that the literary female criminal is a fundamentally different portrayal because she breaks the "mad-bad" woman dichotomy that dominates both legal and medical discourses on female criminality. I show that the criminal femme fatales' negotiations of female agency within hardboiled crime fiction fluctuate and shift between the two poles of the criminalized and the medicalized women. These criminal femme fatales exhibit culpability in their actions that bring them into an encounter with the criminal justice system and resist being pathologized as women who suffer from a psychological ailment that affect their control. The thesis concludes that the ways in which the criminal femme fatales trouble normative socio-cultural conceptions relating to docile femininity and passive sexuality, not only destabilize the totality and fixity of the stereotype of the femme fatale in hardboiled crime fiction, but also open up broader debates about the representation of women in popular culture and the intersections between genre and gender.