The study is an empirical investigation into the implementation of a variety of grouplearning structures in an online translation classroom. Drawing on the academic literature in the fields of translation didactics, social constructivism and e-learning, it describes the design and implementation of an online module in economic translation at Dublin City University during the academic years 2003/4 and 2004/5. The main body of the work evaluates the comparative strengths and weaknesses of three group-learning structures implemented in the online module. These are labelled 'discussion groups', 'cooperative groups' and 'collaborative groups' respectively. A case-study approach is adopted in the study, with transcripts of online discussions representing the main data source. These are analysed using the 'Community of Inquiry' Model, a content analysis model derived from the research literature on Web-based learning. Findings from this analysis technique are triangulated with numerical measurements of student participation and online interaction, and with qualitative evaluation of student perceptions, in order to establish which task structures are most effective in promoting learning on the basis of group interaction via text-based computer conferencing. In addition, the study draws conclusions about the methodologies available for the study of group learning in an online environment, the advantages of Web-based translator training, and the disadvantages and challenges arising from such an approach. The study has a contribution to make on a number of fronts. It explores the implications of designing translation instruction for Web-based delivery, it adds to the literature on online group-learning structures, and it presents a model for instructors and researchers to investigate the quality of the educational experience in an online translation classroom.