This special issue encompasses five papers devoted to the different existing relationships between soft computing branches and classical artificial intelligence. The issue originated from the ‘‘50 years of artificial intelligence: campus in multidisciplinary perception and intelligence, CMPI-2006’’ multi-conference (http:// www.info-ab.uclm.es/cmpi/1024x768/overview.htm), that was held in Albacete, Spain, during 10–14 July 2006, to commemorate the 50th anniversary of the creation of artificial intelligence at the Dartmouth Conference (http://www-formal.stanford.edu/jmc/his tory/dartmouth/dartmouth.html). The topic of the issue, ‘‘The impact of soft computing for the progress of artificial intelligence’’, was associated to one of the four tracks of the said multiconference, ‘‘Artificial intelligence’’, but as guest editors, we did not only want to restrict ourselves to edit an special issue collecting extended versions of some high quality papers selected from CMPI-2006. Instead, we aimed it to become a reference text on the topic and thus we decided to invite eight worldwide recognized researchers on different branches of the soft computing area to write a specialized contribution on the relation between that branch and the ‘‘classical’’ artificial intelligence topic to which it is directly related. Finally, four of those researchers accepted our invitation, as well as four conference contributions were selected and their authors invited to submit a significantly expanded version. These eight original contributions have been thoroughly revised and only five of them were finally accepted to become the papers currently presented in this issue. Unfortunately, the three remaining contributions, all of them corresponding to extensions of the conference papers, were rejected due to the high quality standards we wanted to impose for the special issue. First, we briefly review the scope of the special issue. Afterwards, we give an overview on the contents of the papers in it. Finally, some acknowledgments are presented.