The International Workshop on Hybrid Metaheuristics is now an established event and reaches its fourth edition with HM 2007. One of the main motivations for initiating it was the need for a forum to discuss specific aspects of hybridization of metaheuristics. Hybrid metaheuristics design, development and testing require a combination of skills and a sound methodology. In particular, comparisons among hybrid techniques and assessment of their performance have to be supported by a sound experimental methodology, and one of the mainstream issues of the workshop is to promote agreed standard experimental methodologies. These motivations are still among the driving forces behind the workshop
and, in these four years, we have observed an increasing attention to methodological aspects, from both the empirical and theoretical sides. The papers selected for presentation at HM 2007 are indeed a representative sample of research in the field of hybrid metaheuristics. They range from methodological to application papers. Moreover, some of them put special emphasis on the experimental analysis and statistical assessment of results.