The International Classroom Lexicon Project set out to document the professional vocabulary of middle school teachers within the context of mathematics classes in ten different countries from around the world. The construction of a national lexicon, which can be thought of as the characterisation of a very specific aspect of the culture of each participating country, was undertaken by research teams involving experienced teachers as genuine co-researchers. Each cultural artefact identified the words by which teachers name the classroom phenomena in their respective environment. These are the terms that are used for seeing, describing and communicating about the world that is the middle school mathematics classroom. The national lexicons documented by the country teams varied in number and nature of terms included. The number of terms included in the lexicons range from 57 to 123 (Czech 57; Australia 61; Germany 65; Japan 70; Chile 74; Finland 99; USA 99; Korea 103; France 116; China 123). With regards to the nature of the terms included in the lexicons, country teams described different contextual factors that shaped and influenced the terms they included in their lexicon. These included cultural, historical, educational, and language-based factors.The Australian Lexicon developed through this study consists of sixty-one terms considered familiar to lower secondary school teachers of Mathematics. In this presentation we also report the work conducted by the team of Australian researchers and experienced teachers who identified this professional vocabulary. The lexicon was developed and refined over a number of phases and these are detailed and described. Each lexical term has been operationalised with a description as well as examples and non-examples from the classroom. A process of local and then national validation was used to refine and ratify the lexicon as one reasonable representation of the vocabulary used by teachers to describe classroom phenomena. It was found that the terms of this Australian Lexicon are characterised by their ‘generic nature’, as they are familiar to teachers of other subject areas as well, and, with respect to linguistic form, most of the terms are gerunds and participles.