This paper describes the architecture of the Guide Project, a proposal for innovation of Health Information Systems, putting together medical and organizational issues through the Separation of Concerns paradigm. In particular, we focus on one building block of the architecture: the Guideline Management System handling the whole life cycle of computerized Clinical Practice Guidelines. The communication between the Guideline Management System and the other components of the project architecture is message-based, according to specific contracts that allow an easy integration of the components developed by different parties and, in particular, with legacy systems (i.e. existing electronic patient records). In turn, the Guideline Management System components are organized in a distributed architecture: an editor to formalize guidelines, a repository to store and publish them, an enactment system to implement guidelines instances in a multi-user environment and a reporting system able to completely trace any individual physician's guideline-based decision process. The repository is organized in different levels that can be international, national, regional, down to the specific health care organization, according to the healthcare delivery policy of a country. Different organizations can get Clinical Practice Guidelines from the repository, adapt and introduce them in clinical practice.