Preface:Contrib. Plasma Phys. 3-5/2010

The crucial importance of edge properties of fusion plasmas has been increasingly appreciated over the last decades. The development of plasma edge theory, i.e. of quantitative understanding, is monitored, critically discussed, and stimulated through the bi‐annual series of international workshops on Plasma Edge Theory in Fusion Devices (PET). The 12th PET (PET‐12) was held at the State Museum and Reserve Rostov Kremlin in Rostov Veliky, Yaroslavsky region, Russia, from 2nd to 4th of September 2009. It was carefully organized by the Russian Research Centre Kurchatov Institute. The event was generously co‐sponsored by this Research Centre. Additional financial support came from RFBR, Russia.The Director‐General of the State Museum and Reserve Rostov Kremlin, Prof. A.E. Leontiev, kindly agreed to open the conference with a welcoming address. The participants greatly appreciated the keen backing of PET‐12 by Prof. V.P. Smirnov of the Russian Research Centre. Much of the success of this meeting was based on the enormous load of diligent work carried by the Secretary of the Local Organizing Committee (LOC), Prof. Dmitry Morozov. The great supporting efforts of Dr. L.K. Kuznezova, Dr. M.L. Subbotin and Mr. L.N. Kimchenko of the LOC are particularly appreciated.In six invited summary lectures this time the subjects of ITER divertor design, tokamak edge nonlinear dynamics, pedestal physics, self‐similarity of edge plasma turbulence, theoretical aspects of dust in fusion devices, and non‐diffusive transport in detached plasma conditions have been reviewed. In the distribution according to topic, the number of papers on kinetic and fluid edge plasma simulation, followed by those on neutrals and impurities, and those on SOL turbulence were in the lead. Altogether 57 contributions were brought forward, including 9 as oral presentations, most as posters in three sessions. In addition to being discussed during the workshop, all papers have been screened by peer review. The results have been composed to these Proceedings. Given the importance of the subject for fusion and the ongoing strong international research efforts in this field, it has been decided to organize a next workshop, PET‐13, in USA, during the year 2011