This book gathers contributions presented during an In- ternational meeting organized by the Laboratory of Photobio- logy of the University of Liege, Belgium, on 8 and 9 August 1983. The general topic of the discussions was protochlorophyl- lide reduction and greening. Among the reasons for choosing this topic were the recent advances in the field. These ad- vances deal with: (1) The characterization of the basic constituents of the photoenzymatic complex responsible for protochlorophylli- de reduction. This complex is kwn to be ternary, comprising the pigment: protochlorophyllide, NADPH and the enzyme proto- chlorophyllide oxidoreductase. (2) The discovery of short-lived intermediates in the photoreduction process, and in particular, the recent findings resulting from the proqresses of the picosecond and nasecond spectrometry. (3) The obtention of new data on the components of the plastids, on the changes they undergo during the first steps of greening, and on the distribution of the pigment-protein complexes between the various substructures of the etioplast. (4) The detection of early photoactivities apart from protochlorophyllide reduction. These subjects have ~cen extensively discussed during the meeting and several sections of this book are devoted to the presentation of the new data.