In this thesis, I theorise Contemporary Cinematic I-Witnessing as a critical approach to the production and viewership of autobiographical experience on film. The analysis utilises autobiography, film, and adaptation studies to develop an ethical framework that considers the representation of autobiographical experience on film as a form of testimony. The research reveals the codes and conventions of the autobiographical ‘I’ on screen, to identify and interrogate the cinematic and empathic strategies that invite the viewer to bear witness. Fundamentally, Contemporary Cinematic I-Witnessing describes the unspoken agreement between subject and viewer, underpinned by a singular shared objective: to bear witness to the subjective truth of a life. I argue that the subjective truth of autobiographical experience is conveyed on screen along a continuum of representation. The project begins by exploring selfreflexive film as self-witnessing, or autofilmic testimony, in the analyses of Arirang (Kim, 2011), Tarnation (Caouette, 2003) and Blue (Jarman, 1993), by mapping the first-person modes of address and documentary practices used in these films. The analysis moves on to explore The Tale (Fox, 2018) and Persepolis (2007) as narrative films that further constitute self-witnessing, whilst expanding the critical scope of autofilmic testimony to include the representation of traumatic memory and collective identity as advocacy. The thesis goes on to propose the cinematic adaptation of a literary autobiography as a secondary witnessing project, or auteurbiography, addressing questions of ethics, authorship, and fidelity. Using The Diving Bell and the Butterfly (Schnabel, 2007) to advance the notion of an ethical ‘pact’ between the filmmakers and the autobiographical subject, I argue that fidelity is crucial to the testimonial tone of auteurbiography. The analysis develops to consider issues of cinematic construction, creative authority, and relationality, exploring the hierarchies of authorship, ownership and representation that emerge throughout the adaptive process. The thesis concludes with a comparative case study of Being Flynn (Weitz, 2012) and Julie & Julia (Ephron, 2009), which exposes the limitations imposed by gender, genre, and commercial concerns, and the ways these issues can compromise the testimonial agenda of Contemporary Cinematic I-Witnessing. Contemporary Cinematic I-Witnessing draws together and builds upon existing scholarship within autobiography and film studies, to advance an intersectional and interdisciplinary approach to the analysis of autobiographical and testimonial subjectivity on screen.