The W3C OWL Web Ontology Language has had significant usage in the five years that it has been a W3C recommendation. OWL is just finishing its first revision - OWL 2 is currently a W3C candidate recommendation. To take OWL from its representational roots in Description Logics to its current status has required research in effective representational constructs, the computational complexity of reasoning, algorithms and tools for reasoning, and user interfaces for building ontologies. Just as important have been non-research activites - not only the development of reasoning and user interface tools required to support the above research - but also much work on fitting OWL into the W3C view of the Web, such as merging the semantics of OWL and the semantics of RDF, using datatypes from XML Schema in OWL, and transferring OWL information as XML and RDF. Both kinds of work were vital for the first version of OWL and both kinds of work have remained important in the OWL 2 revision. This talk will describe much of the work underlying OWL, concentrating on the portion of the work most involved with OWL 2.