— In this position paper, we motivate the need for streaming data integration in three main forms including across multiple streaming data sources, over multiple stream processing engine instances, and between stream processing engines and traditional database systems. We argue that this need presents a broad range of challenges and opportunities for new research. We provide an overview of the young state of the art in this area and further discuss a selected set of concrete research topics that are currently under investigation within the scope of our MaxStream federated stream processing project at ETH Zurich.