Building on Orlikowski's reflections on sociomateriality, this article argues that we have to stop separating the material and the social to be able to precisely account for what matters in technology adoption and use, and that one way to do this is to take people's matters of concern seriously. This means two things: taking into account all the matters of concern that come to express themselves in conversations (whether related to tools, rules, documents, principles, etc.) and not just the people who voice them, and showing how some of these concerns start mattering more than others by connecting with other matters of concern. To demonstrate the theoretical and empirical value of this approach, we analyze two interactional episodes taken from our longitudinal study of the introduction of a wiki at the French National Agency for Radioactive Waste Management.