American playwright John Patrick Shanley’s 2004 Pulitzer Prize-winning play Doubt: A Parable is a morality tale that addresses both the elusiveness of certainty and the implications of judging a person’s guilt without proof. Its plot concerns the suspicions of a senior nun, Sister Aloysius, at a Bronx Catholic parochial school in 1964 that her parish’s popular young priest, Father Flynn, has sexually abused the school’s only African-American student. The evidence against the priest is far from conclusive, however, and the play ends without definitively resolving his guilt or innocence, thereby obliging each member of the audience to determine if Sister Aloysius was justified in driving the priest away from his parish. This article examines the ambiguity surrounding Father Flynn in the play and then compares the work with the 2008 film adaptation, which Shanley himself wrote and directed, viewing the latter as the playwright’s attempt to establish a definitive version of his play. In particular, this article demonstrates how the adaptation, through a number of new scenes and a much larger cast of characters, carefully maintains the play’s ambiguity with respect to Father Flynn’s guilt or innocence. The article also demonstrates how the film, partly through the use of visual means, underlines how the same event can be interpreted in different ways, thereby further illustrating the elusiveness of certainty.