Instantiating a resource of an IT-service includes: analyzing a service model including nodes representing resources and being indicative of a resource type, each node comprising a generic API providing at least one abstract method for instantiating the resource represented by the respective node. For each node, determining the resource type indicated by the node; evaluating a service provider catalog indicative of a resource manager operable to provide a resource of a given resource type and determining an address of the resource manager; selecting a resource manager; sending a request to the address of the selected resource manager for a description of a resource-manager-specific API of the resource manager; receiving the requested description from the selected resource manager; overriding the abstract method by a resource-manager specific method of the resource-manager-specific API for instantiating the resource; and executing the overridden abstract method for instantiating the resource represented by the node.