The stereoprojection on the cover shows the structure of a double-helix strand in solid α-amylose. In the ball-and-stick model in the upper part, C is symbolized by pink spheres, O by orange spheres. However, what is the significance of the curved surface, one side of which is blue, the other side green, in the lower part? This surface represents a non-Euclidian, periodically curved potential surface (of the type Q*). In general, the space in crystalline mateirals is divided up by such surfaces. The structural fragments thereby obtained can be analyzed as increments with respect to their chemical significance. This results in a better understanding of the collective behavior of such substances. Further details on this fundamentally new approach to structural chemistry, whose results are also of special aesthetic appeal, are described by H. G. von Schnering and R. Nesper on P. 1059 ff.