Continuous data streams arise naturally, for example, in the network installations of large Telecom and Internet service providers where detailed usage information from different parts of the network needs to be continuously collected and analyzed for interesting trends. This talk will provide an overview of the key research results surrounding the systems issues in data stream processing. I will overview recent results on data stream system architectures, query processing, languages for querying data streams, and complex event processing. I will conclude with some open research questions in these areas.