He has participated in numerous European and Greek research projects dealing with the design, implementation and validation of communication networks. He has been mainly involved in the following projects: RACE 1014 (ATMOSPHERIC), RACE 2016 (STRATOSPHERIC), ESPRIT 5193 (MAXI, Metropolitan Area Communication System), ESPRIT 7314 (MANTIS, Metropolitan Area Network for Integrated Services). From 1996 to 1999 he has been working in the area of Service Creation over Open Distributed Platforms. In this area he has participated the ACTS projects ABS (AC206) and in the ACTS project ABROSE (AC316). In the framework of the IST Programme of the European Community he has been involved in the IST projects ANDROID, FAIN, CAUTION and CAUTION++. He was the scientific co-ordinator of several Greek research projects. His research interests include: active networks, nomadic computing, performance evaluation and traffic engineering, resource management for fixed and wireless networks. Dr. Karetsos is a member of the Technical Chamber of Greece, and of the Greek Association of Mechanical and Electrical Engineers.

 He has served as a reviewer and member of the Technical Committee for various conferences and journals within his scientific interests. Overall he has participated in the organizational aspects of the following international conferences:

1. EDOC (Enterprise Distributed Object Computing) 1998, San Diego, California, USA 
2. IS&N (Intelligence in Services and Networks), Antwerp, Belgium 1998
3. EDOC (Enterprise Distributed Object Computing) 1999, Mannheim, Germany
4. DSOM (Distributed Systems: Operations & Management), Austin, Texas, 2000
5. COMCON 8 (8^th International Conference on Advances in Communications and Control), Crete, Greece 2001
6. IST Mobile & Wireless Communications Summit, Barcelona, Spain, 2001
7. IWAN (International Workshop on Active Networks) 2001, Philadelphia, Pennsylvania, USA
8. Radio Network Management & Mobile Location Workshops 2002, Athens, Greece
9. IST Mobile & Wireless Communications Summit, Thessaloniki, Greece, 2002
10. Radio Network Management & Mobile Location Workshops 2004, Athens, Greece
11. IST Mobile & Wireless Communications Summit, Aveiro, Portugal, 2003
12. IST Mobile & Wireless Communications Summit, Lyon, France, 2004
13. European Wireless 2005, Nicosia, Cyprus
14. IST Mobile & Wireless Communications Summit 2005, Dresden, Germany
15. IEEE PIMRC 2005, Berlin Germany
16. First Wireless Euro-Mediterranean International Conference (WEMIC 2006), Amman, Jordan
17. European Wireless 2006, Athens, Greece
18. CCDN 2006 (Content Caching and Distribution Networks), in conjunction with Networking 2006 IFIP Conference
19. IST Mobile & Wireless Communications Summit 2006, Myconos, Greece, 4-8 June 2006
20. TEMU 2006, International Conference on Telecommunications and Multimedia, Crete, Greece
21. IEEE PIMRC 2006, Helsinki, Finland
22. Mobile Computing and Wireless Communications International Conference (MCWC 2006),
23. The Fifth IASTED International Conference on COMMUNICATION SYSTEMS  AND NETWORKS (CSN 2006) August 28-30, 2006, Palma de Mallorca, Spain
24. IST Mobile & Wireless Communications Summit 2007, Budapest, Hungary, 1-5, July 2007
25. IEEE PIMRC 2007, Athens, Greece, 3-6, September 2007
26. 4^th Mobility Conference, International Conference on Mobile Technology, Applications and Systems 12-14 September 2007, Singapore
27. IEEE International Symposium on Wireless Communication Systems 2007, 17-19 October 2007, Trondheim, Norway
28. MM-CNIT 2007, Multi-Conference on Communications, Networking and Information Technology, 6-8 December 2007, Amman, Jordan
29. MediaWiN 2008, Third Workshop on multiMedia Applications over Wireless Networks, July 6th, 2008, Marrakech, Morocco
30. TEMU 2008, International Conference on Telecommunications and Multimedia, 16-18 July 2008, Ierapetra, Crete, Greece
31. 5^th Mobility Conference, International Conference on Mobile Technology, Applications and Systems, Yilan, Taiwan, September 10-12, 2008.
32. IEEE PIMRC 2008, 19^th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, September 15-18, Cannes, France
33. 3rd IEEE International Workshop on Modeling Autonomic Communication Environments (MACE 2008) September 25-26, 2008, Samos Island, Greece
34. WCNC 2009, IEEE Wireless Communications & Networking Conference, 5-8 April 2009, Budapest, Hungary
35. IST Mobilight, 1st International Conference on Mobile Lightweight Wireless Systems, Athens, Greece, May 18-20, 2009
    
36. MediaWiN 2009, Fourth Workshop on multiMedia Applications over Wireless Networks, 5 July 2009 - Sousse, Tunisia

37. IEEE PIMRC 2009, 20^th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, September 13-16, Tokyo, Japan
38. EW2011, 17th European Wireless Conference, April 27-29, 2011, Vienna, Austria
39. IEEE VTC 2011 Spring, 73rd Vehicular Technology Conference, May 15-18 2011, Budapest, Hungary
40. ΙΕΕΕ ICT 2011, 18th International Conference on Telecommunications, May 8-11, 2011, Ayia Napa, Cyprus
41. IEEE ISCC 2011, The 16^th IEEE symposium on Computers and Communications, June 28 - July 1, 2011, Corfu, Greece