This paper reports on the design of a collaborative system to support citizens' advisory services. Recent research on the adoption of collaborative technologies indicates that: a) successful collaborative technologies diffuse from the private sector to the business sector and not vice versa, b) collaborative processes evolve and therefore cannot be prestructured in detail, and c) creative collaboration can be characterized as creating and sharing mental models. We demonstrate how these insights informed our design of a citizens' advisory system and provide data from an evaluation in a German city. Implications for the design of our collaborative system are offered.