Crystallisation of materials is a key step in chemical synthesis as a means of purification and phase separation. However, the initial stage of crystallisation, involving nucleation of molecules to form molecular clusters from a supersaturated solution is not fully understood. The results from this work will elucidate the thermodynamics and kinetics associated with such processes and the effect this has on the crystal properties, e.g. polymorphic form, and growth rate. This experiment will build on SAXS data using para aminobenzoic acid as a representative material, to probe the structural evolution of single molecules to molecular clusters through to nano-sized crystallites. SAXS results suggested a mechanism involving progression from monomer through dimers to more extended structures. SANS will be used to probe both the low-Q region which could not be elucidated from SAXS data and also the high-Q region where evidence suggesting the presence of pre-nucleation clustering, which have been previously predicted and are critical to fully elucidating the crystallisation mechanism. SANS will be used to elucidate the structure/ dynamics of such intermediate systems.