Many of the benefits of computerized physician order entry (CPOE) stem from its ability to support medical decision-making and error-reduction during patient care. This automated "intelligence" is typically represented by a network of rules. We describe a taxonomic representation of clinical decision-support rules in the context of developing and implementing a de novo CPOE and decision-support system. In our experience, this clinical rules taxonomy facilitated our implementation goals in the areas of physician acceptance and approval, rules construction and maintenance, and technical development and testing. This rules taxonomy may eventually be used to establish standards by which CPOE-based decision-support is measured.