This dissertation examines the contradictory status of immaturity in our culture. While immaturity’s otherness to heteronormative adulthood is a source of fear and anxiety, this otherness is also what makes it desirable–that is, immaturity represents an escape from the pressures and standards of adulthood, signifying an oppositional subjectivity reminiscent of youthful rebellion. Indeed, the oppositional nature of immaturity is ultimately what gives it power as a source of political agency. Rather than seeing immaturity as something to be ashamed of, or as something to be avoided or defeated, this dissertation, following Judith/Jack Halberstam, views immaturity as a powerful form of resistance as well as a queer “way of being.” In fact, these two latter elements–resistance and queerness–go hand-in-hand; queerness within this project is primarily understood as an uncompromising “resistance to regimes of the normal,” specifically those pertaining to maturity and success. Beginning with a focus on male immaturity, I establish the fear/desire dynamic characterizing the immature male through close readings of the 1950s male-centered melodrama, combined with an historically-oriented analysis of postwar American culture. Next, I examine how comedy and dramedy films about childish men from the 1980s to the present day are also structured by this contradictory dynamic, as they both resist and reinforce heteronormative adulthood. My textual analysis of these films are grounded in theories of queer temporality. Finally, I focus on the female counterpart to the immature male, examining various constructions of female immaturity in recent cinema. Here, I utilize a broader range of queer temporal theories to demonstrate the political potential of immature womanhood, where “immature” gains agency through its queer and feminist resistance to the tyranny of heteronormative adulthood. While this dissertation ultimately seeks to demonstrate how immaturity functions as a site of resistance to (hetero)normativity, it also acknowledges how it can (specifically in the context of male homosociality), reinforce and reproduce oppressive structures, further underlining immaturity’s incongruous status.