This thesis makes a bisexual theoretical intervention in film studies that foregrounds the centrality of transgression in figuring bisexuality on screen. Cinema's bisexual transgressors are mutable and persistent figures appearing across disparate contexts. Although their prevalence on film has been noted in some bisexual criticism, these have often been limited to censures of 'bad bisexual representation'. Alternatively, I follow the lines of critical bisexual thought proposed by Maria Pramaggiore, Jo Eadie, Beth Carol Roberts, and Maria San Filippo, which interrogate the relationship between bisexuality and cinema's structures of sexual signification. My intervention in this dialogue stresses transgression as a central component in conveying screen bisexualities, which are regularly figured through violations of social, political, ethical, and aesthetic rules. I make the case for bisexual transgression's importance in theorising screen sexuality with attention to four cinematic contexts between the 1970s and 1990s, and close readings of four films herein. I consider 'Vampyres' (José Ramón Larraz, 1974) in relation to 1970s les(bi)an vampire film; 'She Must Be Seeing Things' (Sheila McLaughlin, 1987) in relation to 1980s and 1990s lesbian feminist narrative cinema; 'Savage Nights' (Cyril Collard, 1992) in relation to male bisexuality in European art cinema in the context of HIV/AIDS; and 'Basic Instinct' (Paul Verhoeven, 1992) in relation to Hollywood and direct-to-video erotic thrillers from the 1980s and 1990s. Despite these contexts' various dissimilarities, all share an investment in the bisexual as a figure in whom tensions around sexual taxonomy are broached. These figures' sexual transgressions are often multiplied in their alignment with or metaphorisation through other forms of social, political, or ethical forms of transgression. Further, insofar as monosexuality (attraction towards people of a single gender) is naturalised on film through formal conventions, bisexual figuration often involves attendant formal transgressions. To this end, I interrogate the interrelation between bisexual figuration and systems of cinematic temporality, space, and mise-en-scène. My analysis also considers these cinemas' historical contexts and their interactions with the proliferation of bisexuality as a discursive, social, and political formation between the 1970s and the 1990s. Histories of genre, activism, (geo)politics, and theory are drawn upon to identify these cinemas' historical import with specificity. Throughout the thesis, I engage with the contributions of feminist and queer theory to film studies, while stressing the enduring relevance of bisexual theory, which provides rich yet underexploited frameworks through which to approach the sexual politics of cinema. Bisexual figures of transgression populate critical bisexual writing and, by transposing these ideas to the realm of film studies, I consider how bisexuality's troubling of dominant notions of sexual epistemology is figured cinematically. My thesis thus contends that queer film studies is fundamentally impoverished without attention to cinema's bisexual transgressors. These figures-in whom sexuality's potential for mutability, the allure of the forbidden, and the precarity of sexual signification are illuminated-beckon a radically recalibrated mode of enquiry into cinematic sexuality.