| Andreas Angelakis, National Foundation for Agricultural Research, Heracleion, Greece | Research collaboration; coauthoring of papers; collaboration in guest editorship of conference proceedings and journal special issues |
| Sivakumar Belie, University of California Davis, USA | Visit to Itia and lecture in Jun. 2000 |
| Günter Blöschl, University of Technology, Vienna, Austria | Research collaboration and coauthoring of a paper |
| Luigia Brandimarte, UNESCO-IHE, Delft, Netherlands | Research collaboration and coauthoring of a paper |
| Richard Chandler, University College London, UK | Research collaboration in a UK project |
| Tim Cohn, U.S. Geological Survey, Reston, Virginia, USA | Research collaboration and coauthoring of papers |
| Graeme Cox, Hydro Tasmania Consulting | Research collaboration and coauthoring of a paper |
| Christophe Cudennec, INRA, Agrocampus Rennes, France | Research collaboration and coauthoring of a paper |
| Giuliano Di Baldassarre, UNESCO-IHE, Delft, Netherlands | Research collaboration and coauthoring of a paper |
| Abebe Dinku, Addis Ababa University, Ethiopia | Visit to NTUA and collaboration agreement in Oct. 2001 |
| Theodore Endreny, University of New York, USA | Invited lecture in NTUA in Jun. 2006 |
| Efi Foufoula-Georgiou, University of Minnesota, USA | Hosted by Itia during her sabbatical leave (1992-93 and 2000-01); research collaboration and coauthoring of a paper |
| Cate Gardner, IAHS Press | Collaboration with Demetris Koutsoyiannis within IAHS Press |
| Aris Georgakakos, Georgia Tech, Atlanta, USA | Hosted Demetris Koutsoyiannis during his sabbatical leave in Dec. 2005 – Jan. 2006; research collaboration and coauthoring of papers; visit to NTUA/Itia and lecture in 1999 |
| Kostas Georgakakos, Hydrologic Research Center, San Diego, USA | Hosted Demetris Koutsoyiannis during his sabbatical leave in Sep.-Nov. 2005; research collaboration and coauthoring of papers; invited lecture in NTUA in Sep. 2006. |
| Salvatore Grimaldi, University of Tuscia, Italy | Research collaboration within the Statistical Hydrology group of IAHS; collaboration in guest editorship of journal special issues. |
| Vijay Gupta, University of Colorado | Invited lecture in NTUA in Jun. 2006 |
| Entin Hidayah, Institute of Technology Sepuluh Nopember Surabaya, Indonesia | Visit to Itia in Jan.-Feb. 2010 |
| Valerie Isham, University College London, UK | Research collaboration in a UK project |
| Akira Kawamura, Tokyo Metropolitan University (TMU) | Visit to Itia in Jun 2010 and invitation of Andreas Efstratiadis to deliver a lecture in TMU in Nov. 2010 |
| Vít Klemeš, Environment Canada, National Hydrology Research Institute | Research collaboration; visit to Itia and lecture in 2005 |
| George Koukis, University of Patras | Research collaboration and coauthoring of a paper |
| Antonis Koussis, National Observatory of Athens | Research collaboration and coauthoring of papers |
| Zbigniew Kundzewicz, Polish Academy of Sciences, Poznań, Poland & Potsdam Institute for Climate Impact Research, Potsdam, Germany | Co-editorship of Hydrological Sciences Journal with Demetris Koutsoyiannis; research collaboration and coauthoring of papers |
| Christian Leduc, IRD, UMR G-EAU, France | Research collaboration and coauthoring of a paper |
| Harry Lins, U.S. Geological Survey, Reston, Virginia, USA | Research collaboration and coauthoring of papers |
| Federico Lombardo, University of Rome III | Visit to Itia in Mar.-Oct. 2010; research collaboration; coauthoring of papers |
| Cedo Maksimovic, Imperial College | Research collaboration and coauthoring of papers |
| Larry Mays, Arizona State University, USA | Research collaboration and coauthoring of papers |
| Katerina Mazi, National Observatory of Athens | Research collaboration and coauthoring of papers |
| Alberto Montanari, University of Bologna, Italy | Hosted Demetris Koutsoyiannis during his sabbatical leave in Spring 2006; research collaboration and coauthoring of papers |
| Valeria Montesarchio, University of Rome "Sapienza", Italy | Research collaboration and coauthoring of papers |
| Naoko Nakagawa, Tokyo Metropolitan University (TMU) | Visit to Itia in Jun 2010 |
| Francesco Napolitano, University of Rome "Sapienza", Italy | Hosted Demetris Koutsoyiannis during his sabbatical leave in Sep.-Oct. 2008; Research collaboration and coauthoring of papers |
| Paul Northrop, University College London, UK | Research collaboration in a UK project |
| Christian Onof, Imperial College | Research collaboration and coauthoring of papers; invited lecture in NTUA in Jun. 2007 |
| Sanguan Patamatamku, University of Naresuan, Thailald | Visit to Itia in Jul. 2005 |
| Geoff Pegram, University of Natal, South Africa | Visit to Itia and lecture in Jul. 1996 |
| Domenico Piccolo, University of Naples Federico II, Italy | Collaboration in guest editorship of journal special issues. |
| Amilcare Porporato, Duke University, Durham, N. Carolina, USA | Invited Demetris Koutsoyiannis to Duke University in Jan. 2006 |
| Pedro Restrepo, Optimal Decision Engineering Corporation, Boulder, Colorado, USA | Research collaboration and coauthoring of a paper |
| Maura Rianna, University of Rome "Sapienza", Italy | Visit to Itia in Mar.-Jul. 2010; research collaboration; coauthoring of a paper |
| Andreas Schumann, Ruhr-University Bochum, Germany | Collaboration in guest editorship of a journal special issue. |
| Slobadan Simonovic, University of Manitoba, Canada | Visit to Itia and lecture in 1994 |
| Crispin Smythe, Hydro Tasmania Consulting | Research collaboration and coauthoring of a paper |
| Sarintip Tantanee, University of Naresuan, Thailald | Visit to Itia in Jun.-Jul. 2005 |
| George Tchobanoglous, University of California Davis, USA | Research collaboration and coauthoring of papers |
| Dimitrios Tolikas, Aristotle University of Thessaloniki | Research collaboration and coauthoring of papers |
| Elena Volpi, University of Rome III | Research collaboration and coauthoring of papers |
| Frances Watkins, IAHS Press | Collaboration with Demetris Koutsoyiannis within IAHS Press and Hydrological Sciences Journal |
| Howard Wheater, Imperial College, London, UK | Hosted Demetris Koutsoyiannis during his sabbatical leave in Sep. 1999-Jan. 2000; research collaboration and coauthoring of papers |
| Huaming Yao, Georgia Tech, Atlanta, USA | Research collaboration and coauthoring of a paper |