Humanity now finds itself faced with highly complex challenges – ranging from climate change, and the spread of disease to international security and scientific collaborations - that require effective collective multi-disciplinary decision making with large communities that are distributed in time and space. While social computing tools (e.g. web forums, wikis, email, instant messaging, media sharing sites, social networking, and so on) have created unprecedented opportunities for connecting and sharing on a massive scale, they still fare poorly when applied to deliberation, i.e. the systematic identification, evaluation, and convergence upon solutions to complex problems. Internet-mediated discussions are instead all-to-often characterized by widely varying quality, poor signal-to-noise ratios, spotty coverage, and scattered content, as well as dysfunctional dynamics for controversial issues. This talk will present a novel integration of ideas taken from social computing and argumentation theory that has, we believe, the potential to address these limitations. I will describe the underlying concepts, the results of our evaluations to date, and some promising directions for future work.