This book defends an account of ambiguity which illuminates the aesthetic possibilities of film and the nature of film criticism. Ambiguity typically describes the condition of multiple meanings. But we can find multiple meanings in what appears unambiguous to us. So, what makes ambiguity ambiguous? This study argues that a sense of uncertainty is vital to the concept. Ambiguity is what presses us to inquire into our puzzlement over a movie, to persistently ask "why is it as it is?" Notably, this account of the concept is also an account of its criticism. It recognises that a satisfying assessment of what is ambiguous involves both our reason and doubt; that is, reason and doubt can work together in our practice of reading. This book, then, considers ambiguity as a form of reasonable doubt, one that invites us to reflect on our critical efforts, rethinking the operation of film criticism.