Asynchronous online dialogue offers advantages to learners, but has appeared to involve only limited use of new literacy practices. To investigate this, a multimodal approach was applied to asynchronous dialogue. The study analysed the online discussions of small groups of university students as they developed collaboratively authored documents. Sociocultural discourse analysis of the dialogue was combined with visual analysis of its structural elements. The groups were found to employ new literacies that supported the joint construction of knowledge. The documents on which they worked together functioned as ‘improvable objects’ and the development of these was associated with engagement in ‘attached dialogue’. By investigating a wider range of conference dialogue than has previously been explored, it was found that engaging in attached dialogue associated with collaborative authorship of improvable objects prompts groups of online learners to share knowledge, challenge ideas, justify opinions, evaluate evidence and consider options.