In my study of interpreters of Australian Sign Language (Auslan) to English, I found that interpreters' production of omissions was influenced by their familiarity with the context of the situation and the content of the message they were interpreting, which was a university lecture (Napier 2002). They made a range of omissions; some were strategic, some were based on a reason, and some were errors. I determined that an omission had occurred "when information transmitted in the source language with one or more lexical items does not appear in the target language, and therefore potentially alters the meaning" (Napier 2002, 121). I found that the interpreters involved in the study had high levels of awareness in respect to the omissions they made and why they made them. This type of awareness is called metalinguistic awareness and can be defined as "the ability to focus attention on language and reflect upon its nature, structure and functions" (Garton and Pratt 1998, 149). It also includes the abilities to select and process specific linguistic information and to consider what aspects of language are relevant in any particular context. It can be argued, therefore, that interpreters ought to develop this type of awareness so that they can make the most appropriate linguistic choices and decisions in order to render the best possible interpretation within a particular context. To benefit interpreter educators, I used my research findings to develop an analysis tool for teaching interpreting students to identify the "omission potential" of an interpreting assignment or an interpreted message and the factors that may influence the types of interpreting omissions they produce and why. This chapter introduces an omission taxonomy and step-by-step process of analysis that can be used with students to identify patterns of omissions and the factors that might influence their choice of what to omit and when. By tapping into students' metalinguistic awareness, interpreter educators can actually encourage students to reflect on the reasons omissions were made and the impact of the omissions on interpreted messages.