In a number of recent biology meetings, plant growth factors have been a favorite topic. One may ask if a new colloquium devoted to the metab olism and the activities of cytokinins, considered at the molecular level, was really necessary and will add anything important to the previous contributions. As a matter of fact, the primary purpose of the organizers, of the French National Center of Scientific Research, and of the National In stitute of Agronomic Research which sponsored the colloquium was less the edition of a proceedings book than the desire to bring together a number of scientists who had made contributions towards solving prob· lems in cytokinin research and thereby to provide an opportunity for fruitful discussions without restrictions in the timetable. Indeed this primary target was attained. Moreover, important new fmdings and con clusions were presented by the participants that merited publication in the form ofthis book. It is beyond the scope of this foreword to adver tize or even to classify these new fmdings. We shall only mention a few of them. The reader will appreciate the contributions of those authors who worked hard to elucidate the biosynthetic pathways of natural cytokin ins.