Ambient Intelligence as a vision for future information systems is currently receiving more and more attention in research and industry. In this article, we investigate how related technology domains, such as Artificial Intelligence, Multi-Agent Systems and the Semantic Web can provide methods and IT infrastructures to support Ambient Intelligence middleware and applications. By means of three case studies ranging from personal assistance to megacity management we identify functional and non-functional requirements. Based on this study we propose AmIRA as an Ambient Intelligence Reference Architecture with a focus on methods, architectures and components. We illustrate the instantiation of AmIRA by describing the implementation of three industrial applications related to the previously presented case studies.