Ontolog
- Ontolog is an open, international, virtual community devoted to advancing the field of ontological engineering and semantic technologies, and advocating their adoption into mainstream applications and international standards.
- http://ontolog.cim3.net/

Ontology Engineering: a survey and a return on experience
- Research report by INRIA, presenting the state of the art of engineering techniques and a project description. (downloadable PDF)
- http://www.inria.fr/rrrt/rr-4396.html

Ontologies For Education
- A topic-map driven portal focused on application of ontologies and similar technologies to educational domains.
- http://iiscs.wssu.edu/o4e/

Ontology is Overrated: Categories, Links, and Tags
- Clay Shirky explores online categorization, contrasting ontologies with folksonomies.
- http://shirky.com/writings/ontology_overrated.html

You're It
- A weblog about social tagging.
- http://tagsonomy.com/

Ontologies Come of Age
- Paper by Deborah L. McGuinness discussing ontologies and requirements for their effective use on the web. [2002]
- http://www.ksl.stanford.edu/people/dlm/papers/ontologies-come-of-age-mit-press-%28with-citation%29.htm

Principles of ontology
- Mailing list archive. Some basic definitions by John Sowa.
- http://www-ksl.stanford.edu/onto-std/mailarchive/0136.html

OWL Web Ontology Language Reference
- Detailed description of the OWL W3C specification.
- http://www.w3.org/TR/owl-ref/

Ontology Engineering Background
- Overview of methodologies, papers and people.
- http://www.aifb.uni-karlsruhe.de/WBS/cte/ontologyengineering/

Adaptive Path - Metadata for the Masses
- Discussion of the promise and problems of classification systems created by nonprofessionals.
- http://www.adaptivepath.com/publications/essays/archives/000361.php

European Centre for Ontological Research (ECOR)
- ECOR represents a new approach in applying ontology to a variety of problems in information science and related areas, by coordinating institutions, organisations and companies working in the field.
- http://www.ecor.uni-saarland.de/

CO-ODE
- Collaborative Open Ontology Development Environment is a project led by the Medical Informatics Group at the University of Manchester.
- http://www.co-ode.org/

Buffalo Ontology Site
- Large collection of links and papers about Contemporary Ontology, History of Ontology and Ontological Engineering. From the Department of Philosophy, State University of New York.
- http://ontology.buffalo.edu/

WonderWeb : Ontology Infrastructure for the Semantic Web
- A project aiming at large-scale deployment of ontologies as the foundation for the Semantic Web.
- http://wonderweb.man.ac.uk/index.shtml

Ontoweb
- The community site for Ontoweb, a European Union founded project about Ontology-based information exchange for knowledge management and electronic commerce.
- http://www.ontoweb.org

On-To-Knowledge
- A project of the European Information Society Technologies, under 5th Framework Program (1999-2002). The project develops knowledge management methods and tools, based on ontology sharing and reuse.
- http://www.ontoknowledge.org/

Knowledge-Base and Ontology Projects Worldwide
- A catalog of links to projects, tools, and events.
- http://www.cs.utexas.edu/users/mfkb/related.html