The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal–organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

The preparation of co-crystals via mechanochemistry combines the quest for clean and green processes with the investigation of multicomponent new materials, among the currently most fashionable systems in the crystal engineering field: the physico-chemical properties of the components add, merge or transform when co-crystals are formed, giving rise to potentially improved performance in “old” solid-state chemistry fields, as in the pharmaceutical industry field, where they represent a way to obtain new formulations and to improve the properties (solubility, thermal stability, compressibility, etc.) of both new and existing drugs.

The articles and highlights presented at the second CrystEngComm meeting, held in Nottingham in September 2004 are reviewed. The discussion has highlighted the current development of crystal engineering and allowed to emerge some of its future potentials. In particular, the papers described in this highlight focus on four fundamental aspects: (i) intermolecular interactions: evaluation and application to crystal design; (ii) networks: design and applications; (iii) approaches to crystal synthesis; (iv) polymorphism, solvates and chiral crystal resolution.

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.