Creating software systems by composing already existing reusable software is a vision which has been driving the development of software technologies and paradigms for a long time. By combining visual modelling and service oriented architecture, this thesis proposes a visual language for composition of heterogeneous service, called AuSCL (Another unified Service Composition Language). The thesis presents requirements for service composition in general, and additional requirements introduced by the use of heterogeneous service technologies. Existing visual languages such as UML2 and BPMN has been investigated and evaluated in three case studies. This has lead to a list of potential improvements for UML2 and BPMN which have been used in the design of AuSCL. AuSCL is a UML2 profile, introducing a set of stereotypes to enhance UML2 functionality and a domain specific structure of model views for modelling a heterogeneous service composition from a set of viewpoints. This structure consists of a set of model views and are introduced to narrow the extensive modelling possibilities provided by UML2. The model views are divided into abstract and concrete views, and does also separate between internal and external aspects. AuSCL extends UML2 to support dynamic service selection (service discovery and and runtime selection) for late binding and a consistent way of combinig activities and interactions to model communication. AuSCL is evaluated against the identified requirements and by implementation of the same case studies used in the evaluation of UML2 and BPMN. The evaluation shows that AuSCL is better suited than UML2 and BPMN for visual modelling of heterogeneous service composition for the identified requirements and case studies.