The introduction of Information and Communication Technologies (ICT) into public administrations has been radically changing the way organizations cooperate and, more generally, the way to think about business processes over organizational boundaries. In this paper we describe our approach to combining business processes with business rules in order to integrate effectively single units in an inter- or intra-organizational cooperation. Business rules represent the knowledge that an administration has about its business; with regard to this, they can express strategies, contracts and can influence not only staff relations, but, finally, citizen relations, as well. In other words, business rules are the core of an administration and affect either the business processes or the behaviours of the system participants. They are typically expressed implicitly in business contracts and they are embedded within the source code of many application modules. So a concise and declarative statement of business behaviour is converted into a set of programming instructions, which are spread widely throughout the whole information system. In this way, business rules are difficult to change and keep consistent over the time. For this reason, it is necessary to reengineer the system in order to logically and perhaps physically externalize rules from the application code. In our proposed approach, we describe a cooperation as a collection of tasks combined in certain ways according to the organization logic specified by business rules. Our rule-driven methodology has the goal to make the business process design more adaptable to the changes of internal or external environment.