% abstract of WWW-2009 conference Tutorial "Rules on the Web" % by Benjamin Grosof, Mike Dean, and Michael Kifer Rules is probably the most important frontier area today for the Semantic Web's core technology and standards, and is a main emerging area of the Web overall. Rules extend databases and ontologies with more powerful, flexible, and active forms of "structured" knowledge (as opposed to "unstructured" knowledge such as text), and have a number of close relationships to other aspects of the overall Web such as services, trust, query/search, and collective intelligence. There are a number of exciting research issues, and web rules functionality is being mainstreamed into core industry products such as Oracle's database suite. Recent progress includes fundamental advances in the underlying knowledge representation techniques and in the integration of rules with ontologies and database query/search; major initial industry standards from W3C and OMG nearing finalization; substantive translations between heterogeneous types of commercial rule engines; development of open-source tools for inferencing and interoperability; a wide range of emerging applications including in business, science, and trust; and accelerating industry investments/acquisitions in the technology including by integrated software companies such as Oracle, IBM, and Microsoft. This tutorial will provide a comprehensive and up-to-date introduction to these developments and to the fundamentals of the key technologies involved. It will explore example application scenarios, overall requirements and challenges, and touch upon business/social value and strategy considerations.