the study of the selectivity of reactions becomes of paramount importance. One can learn quite a lot from Nature, which uses molecular recognition to achieve selec­ tivity in a degree so far unattainable by mere mortals. To analyze the structural features applied by Nature, to accomplish high molecular recog­ nition, and to simulate these features by synthesis have recently become therefore favorite occupations of chemists. The purpose of this conference was to bring together two groups, the analysts and the syntheticists, to discuss the present status of the knowledge. This monograph contains the chairman's introduction in which he has summarized the main points at issue and the contributions of the renowned scientists who participated. The organizers hope that it will stimulate further research in this fascinating field.