The GAP 4 package CrystCat provides a catalog of crystallographic groups of dimensions 2, 3, and 4 which covers most of the data contained in the book "Crystallographic groups of four-dimensional space" by H. Brown, R. Bülow, J. Neubüser, H. Wondratschek, and H. Zassenhaus (John Wiley, New York, 1978). This catalog was previously available in the library of GAP 3. The present version for GAP 4 has been moved into a separate package, because it requires the package Cryst, which is loaded automatically by CrystCat. The benefit of this is that space groups extracted from the catalog now have the rich set of methods provided by Cryst at their disposal, and are no longer dumb lists of generators. Moreover, space groups are now fully supported in both the representation acting from the left and the representation acting from the right.