How can free and equal people cooperate to solve conflicts and common problems in a rational and legitimate way? In this article I deduce principles for doing so from the requirements of rational communication set out in the discourse theory of Jürgen Habermas. I apply them in defining a process of efficient decisionmaking. What I call ‘communicative design’ denotes the design of a reason giving process in which the practice of proposing and assessing claims with regard to rulemaking and problem solving is undertaken on an equal and autonomous basis. Two sets of prescriptions are given: organisational principles for the composition of groups and argumentative principles for deliberation. However, any procedure aimed at achieving a rational consensus in decision making in organisations has to deal in practice with limitations of time, participation and the information available. Communicative design may not guarantee strictly rational decisions, then, but the procedure it constructs does promise relatively ‘more valid’ decisions than might be expected if another procedure had been adopted.