This chapter reviews empirical evidence bearing on the design of online forums for deliberative civic engagement. Dimensions of design are defined for different aspects of the deliberation: its purpose, the target population, the spatiotemporal distance separating participants, the communication medium, and the deliberative process to be followed. After a brief overview of criteria for evaluating different design options, empirical findings are organized around design choices. Research has evolved away from treating technology for online deliberation dichotomously (either present or not) toward nuanced findings that differentiate between technological features, ways of using them, and cultural settings. The effectiveness of online deliberation depends on how well the communicative environment is matched to the deliberative task. Tradeoffs, e.g. between rich and lean media and between anonymous and identifiable participation, suggest different designs depending on the purpose and participants. Findings are limited by existing technologies, and may change as technologies and users co-evolve.