This volume is based on the Second Workshop on Argumentation in Multiagent Systems (Argmas). The workshop was held in conjunction with the 4th Int- national Conference on Autonomous Agents and Multiagent Systems (aamas), at the University of Utrecht in Utrecht, The Netherlands, in July 2005. The workshop itself took place on July 26. We are happy to report that the second workshop was just as popular and successfulasitspredecessor,heldtheprevioussummerinNewYork.Wereceived 17 submissions, eachof which wasreviewed by at least three experts in the ?eld, and ten of these papers were accepted for presentation at the workshop. Once again the workshop was graced by an invited lecture, this time by Frans van Eemeren of the University of Amsterdam, who talked on the subject of prag- dialectics. The workshop attracted 31 participants, ensuring many questions for the speakers, and a healthy exchange of views during the discussion periods. Following the practice established with the post-proceedings of the ?rst Argmasworkshop,weinvitedthepresentersofalltheacceptedpaperstoprepare revised versions of their papers for this volume. In addition we approached - thors of papers on directly related topics that had been presented in theaamas conference, and this gaveus an additionalseven papers. We further solicited one additional paper (details below) and were lucky enough that Prof. van Eemeren consented to send us a paper that covered the material of his invited talk.