J. M. Olson Institute of Biochemistry Odense University OK-5230 Odense M, Denmark Green photosynthetic bacteria have traditionally included only green sulfur bacteria (Chlorobiaceae) and green filamentous bacteria (Chloro- flexaceae), but in this volume are included also the recently-discovered heliobacteria (Gram-positive line), whose reaction centers are strikingly similar to those of the green sulfur bacteria. Two important papers on reaction centers (not included in this volume) have been published recently. Nitschke et al. (1987) have discovered 2 early electron acceptors (Fe-S centers) in the reaction center of Chlorobium limicola, and Shiozawa et al. (1987) have shown that the reaction center of Chloroflexus aurantiacus contains 2 (rather than 3) polypeptides of Mr = 24 and 24.5 kOa respectively. This volume begIns with papers describing structures on the molecular and macromolecular level and events on a picosecond time scale. It ends with papers describing organisms and populations, and events on time scales of hours, days and weeks. The scope of the volume covers biophysics, biochemistry, physiology, ecology, taxonomy and phylogeny. There is only one paper (Ormerod, 1988) dealing with genetics, an area which ought to receive much more attention in the near future.