The design and synthesis of crystalline materials with tailor-made pro
perties is one of the more difficult and therefore challenging tasks i
n supramolecular chemistry. Increasingly, both the properties and the
structures of the molecular building blocks are being optimised prior
to crystallisation, with special emphasis being given to the design of
directional intermolecular interaction sites. Multicomponent systems
such as co-crystals are gaining in attractiveness because they allow g
reater synthetic flexibility and thus enhance diversity in the structu
res and properties of the final crystals. Several new techniques for m
onitoring growth behaviour (often in situ) st the crystal surface have
been reported. There is a clear need to understand in more detail the
fundamental processes taking place in the early stages of the supramo
lecular synthesis.