Cover: The cover picture describes a method for the preparation of well-defined crystallites of MgCl₂-supported Ziegler-Natta catalysts on Si wafers. The growth of the crystallites on the flat silica facilitates their characterization using Electron and Scanning Probe Microscopy. The relative proportions of 120° and 90° edge angles indicate the preference for the formation of a particular crystallite face for the MgCl₂. Polyethylene has been identified to be formed on the lateral faces of the crystallite. Further details can be found in the article by A. Andoni, J. C. Chadwick, H. J. W. Niemantsverdriet, and P. C. Thüne^* on page 1466.-Sponsored by Dutch Polymer Institute.