This volume of Journal of Physics: Conference Series is dedicated to a subset of papers related to the work presented at the 6th edition of the international Workshop on Infrared Spectroscopy and Microscopy with Accelerator-Based Sources (WIRMS), held in Trieste, Italy, September 4–8 2011. Previous editions of the conference were held in Porquerolles (France), Lake Tahoe (USA), Rathen (Germany), Awaji (Japan), and Banff (Canada). This edition was organized and chaired by Stefano Lupi (Roma La Sapienza) and co-chaired by Andrea Perucchi (Elettra), with the support of the Italian Synchrotron Light Laboratory ELETTRA, which was honored to host the WIRMS workshop in its tenth anniversary. The 6th WIRMS edition addressed several different topics, ranging from biochemistry to strongly correlated materials, from geology to conservation science, and from forensics to the study of cometary dusts. Representatives from the infrared scientific programs at synchrotron light sources and free-electron-laser facilities. This edition was attended by 88 participants, including representatives from the infrared scientific programs at synchrotron light sources and free-electron-laser facilities, who enjoyed the stimulating scientific presentations, several detailed discussions, and the beautiful weather and scenery of the Trieste gulf. Participants came from 16 different nations and four continents, including many young scientists, six of which were supported by the organizers. There were 45 scientific talks divided in 11 sessions: Facilities, Microspectroscopy (I, II, III), Time-Resolved Spectroscopies, Extreme Conditions, Condensed Matter, Near-Field, Imaging, THz Techniques and High-Resolution Spectroscopy. 37 posters were also presented at two very lively evening poster sessions. We would like to use the opportunity of writing this preface to thank all the participants of the workshop for the very high level of their scientific contribution and for the very friendly atmosphere, which were the most important keys to the success of the workshop. We also wish to thank all the companies (Bruker, Tydex, Spiricon, Allectra, Neaspec, Micos) and institutions (Sincrotrone Trieste, Sapienza University of Rome, EMS, INFN, CNR-IOM) sponsoring this event. We are indebted to the members of the International Advisory Committee for their valuable help in the difficult choosing of the invited speakers, and for more general advice on the conference organization and structuring. A special acknowledgment goes to the ELETTRA secretary staff, and in particular to Mariella Antonetti, who has been involved with the organization from the very beginning. The 7th WIRMS conference will be held in Melbourne (Australia). Our best wishes go to the organizers for a successful conference. Additional information on the conference can still be found on the conference website: http://www.elettra.trieste.it/events/2011/WIRMS/ A selection of the conference pictures is also available on Flickr: http://www.flickr.com/photos/sincrotronets/sets/72157627705743677/ Guest Editors Stefano Lupi and Andrea Perucchi The PDF also contains details of the Local Organizing Committee and International Advisory Committee and a list of Sponsors.