14th International Conference on Artificial Intelligence: Methodology, Systems, Applications (AIMSA 2010), Varna, Bulgaria, September 8-10, 2010.

International Conference on Software, Services and Semantic Technologies (S3T 2009), Sofia, Bulgaria, October 28-29, 2009.

14th Int’l Conference on Artificial Intelligence in Education (AIED’09), Brighton, UK, July 6-10, 2009 (Conference Workshop Co-Chair)

Seventh Int'l Workshop on Ontologies and Social Semantic Web for E-Learning, in conjunction with 14th Int’l Conference on Artificial Intelligence in Education – AIED’09, Brighton, UK, July 6-10, 2009 (together with Riichiro Mizuguchi, Osaka University, Japan, and Niels Pinkwart, Clausthal University of Technology, Germany)

6th Int'l Workshop on Ontologies and the Semantic Web  for e-Learning (SWEL'08) in conjunction with the Int'l Conference on Intelligent Tutoring Systems – ITS’08, Montreal, Canada, June 23-27, 2008.

5th Int'l Workshop on Ontologies and Semantic Web Services for Intelligent Distributed Educational Systems (SWEL'07) in conjunction with the 13th Int'l Conference on Artificial Intelligence in Education (AIED 2007), Marina Del Rey, California, July 9-13, 2007.

45th ACM Southwest Conference, Winston-Salem, NC, March 18-19, 2007. 

4th Int'l Workshop on Applications of Semantic Web Technologies for Adaptive Educational Hypermediaa (SW-EL'06) in conjunction with the International Conference on Adaptive Hypermedia and Adaptive Web-Based Systems (AH2006), Dublin, Ireland, June 21-23, 2006.

3rd International Workshop on Applications of Semantic Web Technologies for E-Learning (SW-EL'05):
         AI-ED 2005 session: July 18-22, 2005, Amsterdam, The Netherlands.
         ICALT 2005 session: July 5-8, 2005, Kaohsiung, Taiwan.
         K-CAP 2005 session: October 2-5, 2005, Banff, Canada.

2nd International Workshop on Applications of Semantic Web Technologies for E-Learning (SW-EL'04):
         AH 2004 session: Eindhoven, The Netherlands, August 23, 2004.
         ITS 2004 session: Maceio-Alagoas, Brazil, August 30, 2004.
         ISWC 2004 session: Hiroshima, Japan, November 7-11, 2004.

Workshop on Concepts and Ontologies in Web-based Educational Systems, held in conjunction with ICCE 2002, 3-6 December 2002, Auckland, New Zealand.

Eight International PEG Conference "Meeting the Challenge of the New Technologies", Sozopol, Bulgaria, 30 May - 1 June, 1997.

IFIP WG 3.3 Working Conference "Human Computer Interaction and Educational Tools", Sozopol, Bulgaria, 27-28, May, 1997.

Editorships 

Member of the Advisory Board of the IEEE Educational Technologies & Society Journal - ET&S (ISSN 1436-4522) (2004- ).
Associate Editor of the International Journal of Knowledge and Learning - (IJKL) (ISSN 1741-1009) (2006- ). 
Associate Editor of the International Journal of Continuing Engineering Education and Life-long Learning - IJCEELL (ISSN 0957-4344) (2001- ).
Associate Editor of the International Journal of Advanced Technology for Learning - ATL (ISSN 1710-2251) (2003-2005).

Member of the Editorial Board of the International Journal of Metadata, Semantics and Ontologies (IJMSO) (ISSN 1744-2621) (2005- ).
Member of the Editorial Board of the International Journal on Information Technologies and Knowledge (2006- ).
Specialist Reviewer for the International Journal of Artificial Intelligence in Education - IJAIED (ISSN 1560-4292) (2006- ).
Member of the Review Board of the Interactive Multimedia Electronic Journal of Computer-Enhanced Learning - IMEJ (ISSN 1525-9102) (2002- ).

Reviewer and Panelist for the U.S. National Science Foundation
        2002, 2004, 2005, 2006, 2007, 2008, 2009