Gravitational physics has been at the forefront of research in both Astrophysics and Cosmology. Since 1984, relativists in Greece have organized (every two years) a conference that follows progress in this field. The 13th Conference on Recent Developments in Gravity was organized by the relativity group at the Department of Physics of the University of Thessaloniki, in June 2008. This volume contains the written versions as well as extensions of most of the talks delivered at that meeting.

The conference was attended by more than a hundred participants, half of which came from outside Greece, while it brought together nearly all Greek researchers in the areas of relativity, gravity and cosmology. The large number of participants from abroad underlines the increasingly international character of these meetings. In Thessaloniki, the plenary talks and parallel sessions covered topics on gravitational waves, relativistic astrophysics, alternative theories of gravity, mathematical relativity, cosmology and quantum gravity. The plenary speakers were A Ashtekar (Penn-State), G Ellis (Cape Town), V Frolov (Alberta), J Hough (Glasgow), P Laguna (Penn-State), R Loll (Utrecht) and D Psaltis (Arizona). In addition, invited keynote talks were presented by N Batakis (Ioannina), T Christodoulakis (Athens), S Cotsakis (Aegean), P Kanti (Ioannina), L Perivolaropoulos (Ioannina), M Plionis (NOA-Athens), J Pullin (Louisiana), G Siopsis (Tennesee) and M Tsamparlis (Athens).

The Organizing Committee of the conference comprised N Stergioulas (chair), K D Kokkotas, D Papadopoulos, C Tsagas, H Dimmelmeier, K Kleidis, K Zagouris and K Dionysopoulou while the Scientific Committee included N Spyrou (chair – Thessaloniki), P Florides (Dublin) and G Schaefer (Jena). The conference was sponsored by the Aristotle University of Thessaloniki (AUTh), the Department of Physics, the Section of Astrophysics, Astronomy and Mechanics, the Research Committee of AUTh, the Ministry of Macedonia and Thrace, the Ministry of Education and Religious Affairs, the John S Latsis Public Benefit Foundation (http://www.latsis-foundation.org), the ILIAS Network, the Municipality of Thessaloniki, the Prefecture of Thessaloniki and the British Council Greece, to all of which the organizers would like to express their gratitude for the financial and moral support.

The next (14th) conference in this series will take place in the city of Ioannina, organized by the relativity group of the University of Ioannina, in the summer of 2010.

Thessaloniki, 29 August 2009

N Stergioulas and C Tsagas