This study investigates the conventionalization of mouth actions in Australian Sign Language. Signed languages were once thought of as simply manual languages because the hands produce the signs which individually and in groups are the symbolic units most easily equated with the words, phrases and clauses of spoken languages. However, it has long been acknowledged that non-manual activity, such as movements of the body, head and the face play a very important role. In this context, mouth actions that occur while communicating in signed languages have posed a number of questions for linguists: are the silent mouthings of spoken language words simply borrowings from the respective majority community spoken language(s)? Are those mouth actions that are not silent mouthings of spoken words conventionalized linguistic units proper to each signed language, culturally linked semi-conventional gestural units shared by signers with members of the majority speaking community, or even gestures and expressions common to all humans? We use a corpus-based approach to gather evidence of the extent of the use of mouth actions in naturalistic Australian Sign Language-making comparisons with other signed languages where data is available--and the form/meaning pairings that these mouth actions instantiate.