It is hard to give a definition that does justice to the breadth of crystal engineering today. But a useful working description might see modern crystal engineering as the bottom-up construction of functional materials from molecular or ionic building blocks. Crystal engineering has its roots in chemistry with important interfaces with physics and biology, as well as applications in materials sciences, the drug industry and nanotechnology. In short, crystal engineering is a rapidly expanding global discipline practised by scientists with diverse interests in the modelling, synthesis, evaluation and utilization of crystalline solids.