The 20th International Workshop on Optical Waveguide Theory and Numerical Modeling (OWTNM) took place in Sitges, Spain, on April 20–21, 2012.

A total of 28 oral presentations and 10 poster contributions were presented, organized into 8 oral sessions and one poster session. A joint session on Design and Modeling together with the European Conference on Integrated Optics (ECIO) was also organized.

The works covered fundamental aspects of plasmonics, analytical modeling techniques, periodic devices (e.g. photonic crystals, Bragg gratings or sub-wavelength structures) and numerical methods for photonic integrated circuits (PIC) design. A particular highlight was the highly interesting plenary invited talk by Mike Wake (Oclaro Technology), regarding the commercial future of PIC’s.

As usual, the OWTNM workshop provided the ideal environment to promote fruitful conversations among scientists and researchers on these topics. It is sure that a part of the works that will be presented at the next workshop will have born with a friendly conversation with a colleague in a coffee break. We would like to thank to the organizing committee for its outstanding work.

This special issue of OQE includes seven works closely related to oral of poster presentations of the workshop. We want to thank the authors for submitting their work to this special issue and the reviewers for their contribution to improve the quality of this special issue.

The next OWTNM workshop will be held in Enschede, The Netherlands, April 19–20, 2013, on the campus of the University of Twente.