Abstract. In inter-enterprise business service collaborations management of nonfunctional properties has become a fundamental issue, as business management and computing infrastructures are expected to align more closely. Already, serviceoriented computing emphasizes dynamic binding between the functional elements participating in service collaborations and late encapsulation of properties on them. In such environments, the non-functional service properties are used a) as selection criteria during service discovery and b) as parts of collaboration contracts and service-level agreements in particular. This paper contributes to the conceptualisation of non-functional properties in the context of service-oriented computing. The nature of non-functional properties is elaborated by metamodels that formalize the concepts and provide facilities for the management of non-functional properties during design time and run time.