The idea for the p~esent book arose from a 3-day seminar which I organized in March 1984 for young research workers in plant physiology. Participants came from several universities of the French-speaking part of Switzerland and speakers from Basel, Mtinchen, Nottingham, Perpignan, Regensburg, Sheffield, Toulouse, Yale, ZUrich ... and Lausannne. The theme of the seminar was chosen from the range of research fields of our Institute. Meanwhile, feeling it was important to bear in mind that some of our hearers were not specialists in the chosen topic, I wished to pro­ vide a subject that would be of scientific, methodological and epistemologi­ cal interest. The critical analysis of the structural and functional characteristics of plant protoplasts exactly met these criteria. There exists ample material for discussion of the techniques of protoplast preparation, methods used in morphological, biological and biochemical studies, and for the comparison of protoplasts with the cells from which they are obtained.