Data Streams unbounded sequences of time-varying data elements are pervasive. They occur in a variety of modern applications including the Web where blogs, feeds, and microblogs are increasingly adopted to distribute and present information in real-time streams. We foresee the need for languages, tools and methodologies for representing, managing and reasoning on data streams for the Semantic Web. We collectively name those research chapters Stream Reasoning. In this extended abstract, we motivate the need for investigating Steam Reasoning; we characterize the notion of Stream Reasoning; we report the results obtained by Politecnico di Milano in studying Stream Reasoning from 2008 to 2010; and we close the paper with a short review of the related works and some outlooks.