It is the science of what is, the kinds and structures of objects, properties, events, processes, and relations in every area of reality. Ontology is, put simply, about existence. Like so many things, the term was borrowed by computer science and is rapidly becoming a buzzword in industry, tossed about by salesfolk, like all buzzwords, as if it were something everyone knew about. As it turns out, of course, very few people who use the word actually know what it means, and as a result, the actual meaning has changed, and is changing, over time. All computer scientists who claim allegiance to this field are constantly peppered with the same question, "What is an ontology?"

In this issue, I have collected a fairly broad, although by no means exhaustive, sampling of work in the field of ontology research. To define a field is often quite difficult; it is more a collection of people and ideas than it is a specific technology. To represent our field, I present six articles that cover several of the major thrusts of ontology research from the past decade.

In this issue, I have collected a fairly broad, although by no means exhaustive, sampling of work in the field of ontology research. To define a field is often quite difficult; it is more a collection of people and ideas than it is a specific technology. To represent our field, I present six articles that cover several of the major thrusts of ontology research from the past decade.