This volume contains the presentations of the principal speakers at the NATO Advanced Study Institute held at Porto Portese, Italy,23 August - 2 September, 1982. This meeting was the third in a series devoted to the molecular biology of plants. The initial meeting was held in Strasbourg, France in 1976 (J. Weil and L. Bogorad, organizers), and the second in Edinburgh, Scotland in 1979 (C. Leaver, organizer). As in these previous meetings, we have attempted to cover the major topics of plant molecular biology so as to promote the integration of information emerging at an accelerating rate from the various sub-disciplines of the field. In addition, we have introduced several topics, unique to higher plants, that have not yet been approached with the tools of molec­ ular biology, but that should present new and important aspects of plants amenable to study in terms of DNA -+ RNA -+ Protein. This meeting also served to inaugerate the new International Society for Plant Molecular Biology. The need for this society is, like the NATO meetings themselves, an indication of the growth, vitalitv and momentum of this field of research.