There was nothing professional about my first encounter with Yann. It took place thanks to Patrick Seguin and Philippe Jousse who were such good friends that I often forget that we are in the same business. I was so close to Yann that, as paradoxal as it may seem, for a long time I was unable to really appreciate his work in spite of its strength and its originality. While we were organizing the ‘Art on the Beach’ exhibition, our work sessions soon became more personal than professional. Then when we installed Analogies, I realized that there was more to our relationship than just complicity; we had become real collaborators. This catalog is a continuation of that collaboration. The completion of Yann’s ‘light expeditions’ seemed so important to me and to my associates that we gave ourselves completely to the project, aware of how fortunate we were to be able to participate in it. The document that we are publishing today will surely permit other people in other places to discover and appreciate Yann’s work and, we hope, make it possible for him to carry out his projects.