The CSD–450,000 answers … but what are the questions?
A brief survey about the development of knowledge of crystal and molecular structure based on the Cambridge Structural Database (CSD) is given. The CSD may be considered as a database of answers to the question as to which polymorph will form under given crystallization conditions. The emphasis of research over the years has moved from molecular structural geometry, to intermolecular motifs and to wider considerations of crystal packing similarity. Some experimental data items, not recorded in the CSD, place limitations on the usefulness of the CSD, in future research. Unanswered questions are discussed in the areas of crystal structure prediction, polymorphism, co-crystal and solvate formation.