Citizens often face dilemmas where they need to make decisions that impact our lives and are related to science and religion. For example, genetic cloning, nuclear energy and climate change can potentially appeal to moral and religious values as well as scientific knowledge. The ability to coordinate knowledge and values in reaching justified conclusions has thus become increasingly important in contemporary democratic societies. The process of justification of knowledge claims with evidence and reasons is often referred to as 'argumentation'. Curricula of school subjects such as science and religious education (RE) include references to argumentation, and teachers are expected to teach to these standards. Yet, there is often limited opportunity for teachers of conventionally disparate subjects to express their understanding of how argumentation is broadly conceptualised in their own subject and in relation to other school subjects. This paper reports a study investigating how science and RE teachers view the nature of argumentation. The data were drawn from 16 science and 17 RE teachers' survey responses. The findings illustrate how teachers describe both the distinguishing features (e.g. forms of evidence acceptable for substantiating a claim) and similarities (e.g. structures and processes of argument construction) of argumentation in science and RE.