Understanding the appropriation of CSCW-- Tools is key to their successful implementation. This paper explores the social and organizational appropriation of the Cuparla CSCW-environment in the Stuttgart city council. The city council work requires a CSCW design that is based on the notion of digital material in separated work contexts. Within these contexts, the appropriation of technology depends on trust within the collaborating group and the organizational complexity of the tasks the group is working on. Dealing with organizational complexity and trust are therefore fundamental building blocks of CSCW-implementation strategies. With regard to software design, requirements can be elicited, that allow for different social trust structures as well as different task support.