On behalf of the Local Organizing Committee and the International Scientific Committee, we are pleased to invite you to the 20th International Workshop on Plasma Edge Theory in Fusion Devices (PET-20) organized by the KU Leuven, Ghent University and the Laboratory for Plasma Physics, Royal Military Academy. It will be held from Tuesday September 23 to Friday September 26, 2025, at KU Leuven, Leuven, Belgium. The workshop will be fully in-person. Like the preceding workshops, it will reflect the present status of the theory of the edge region in magnetic confinement fusion devices. The workshop will consist of invited lectures, oral presentations and poster contributions. It is recommended that orally presented papers are also accompanied by a poster. The invited and accepted contributed papers will be included in the proceedings of the workshop. The papers will go through the usual refereeing process. Welcome reception and a banquet will take place on the evenings of September 23 and 25, respectively.